diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedBehaviorFixture.Conversions.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedBehaviorFixture.Conversions.cs
deleted file mode 100644
index 8d5609604..000000000
--- a/src/DynamicData.Tests/Binding/WhenPropertyChangedBehaviorFixture.Conversions.cs
+++ /dev/null
@@ -1,344 +0,0 @@
-// Copyright (c) 2011-2025 Roland Pheasant. All rights reserved.
-// Roland Pheasant licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for full license information.
-
-using System;
-using System.ComponentModel;
-using System.Linq.Expressions;
-
-using DynamicData.Binding;
-using DynamicData.Tests.Domain;
-using DynamicData.Tests.Utilities;
-
-using FluentAssertions;
-
-using Xunit;
-
-namespace DynamicData.Tests.Binding;
-
-public sealed partial class WhenPropertyChangedBehaviorFixture
-{
-    /// <summary>Verifies that a numeric conversion is evaluated before reading a property of the converted value.</summary>
-    [Fact]
-    public void NumericConversionBeforePropertyAccess_InitialValue_IsObserved()
-    {
-        // Arrange
-        // An odd numerator produces an exactly representable, non-integral amount.
-        var amount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
-        var model = new ObservablePrice { Amount = amount };
-        var expectedScale = ((decimal)amount).Scale;
-
-        // Act
-        using var subscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale)
-            .RecordValues(out var results);
-
-        // Assert
-        results.Error.Should().BeNull(because: "the next property belongs to the converted decimal, not the source double");
-        results.RecordedValues.Should().Equal(new[] { expectedScale }, because: "the initial value must match the supplied expression");
-        results.HasCompleted.Should().BeFalse(because: "further amount changes remain observable");
-    }
-
-    /// <summary>Verifies that property changes remain observable through a value-changing numeric conversion.</summary>
-    /// <param name="notifyOnInitialValue">Whether subscribing requests an initial value notification.</param>
-    [Theory]
-    [InlineData(false)]
-    [InlineData(true)]
-    public void NumericConversionBeforePropertyAccess_PropertyChanges_AreObserved(bool notifyOnInitialValue)
-    {
-        // Arrange
-        // Odd quarters and eighths have distinct decimal scales without floating-point rounding.
-        var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
-        var changedAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 8d;
-        var model = new ObservablePrice { Amount = initialAmount };
-        var initialScale = ((decimal)initialAmount).Scale;
-        var changedScale = ((decimal)changedAmount).Scale;
-        var expectedScales = notifyOnInitialValue ? new[] { initialScale, changedScale } : new[] { changedScale };
-        using var subscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale, notifyOnInitialValue)
-            .RecordValues(out var results);
-
-        // Act
-        model.Amount = changedAmount;
-
-        // Assert
-        results.Error.Should().BeNull(because: "conversion must be applied on both initial and subsequent chain reads");
-        results.RecordedValues.Should().Equal(expectedScales, because: "notifications must match the expression and initial-value option");
-        results.HasCompleted.Should().BeFalse(because: "amount changes do not complete the observation");
-    }
-
-    /// <summary>Verifies that a numeric conversion at the end of a property path preserves initial and changed values.</summary>
-    [Fact]
-    public void NumericConversionAtLeaf_PropertyChanges_AreObserved()
-    {
-        // Arrange
-        var initialAmount = _randomizer.Double();
-        var changedAmount = initialAmount + _randomizer.Double(1, 2);
-        var model = new ObservablePrice { Amount = initialAmount };
-        var expectedAmounts = new[] { (decimal)initialAmount, (decimal)changedAmount };
-        using var subscription = model.WhenValueChanged(static price => (decimal)price.Amount)
-            .RecordValues(out var results);
-
-        // Act
-        model.Amount = changedAmount;
-
-        // Assert
-        results.Error.Should().BeNull(because: "a conversion must also remain supported as the final expression step");
-        results.RecordedValues.Should().Equal(expectedAmounts, because: "each observed value must be converted to the requested type");
-        results.HasCompleted.Should().BeFalse(because: "further amount changes remain observable");
-    }
-
-    /// <summary>Verifies that a reference cast preserves observation of properties on the runtime model.</summary>
-    [Fact]
-    public void ReferenceCastBeforePropertyAccess_PropertyChanges_AreObserved()
-    {
-        // Arrange
-        var person = Fakers.Person.Clone().WithSeed(_randomizer).Generate();
-        INotifyPropertyChanged model = person;
-        var initialAge = person.Age;
-        var changedAge = initialAge + _randomizer.Int(1, byte.MaxValue);
-        using var subscription = model.WhenValueChanged(static source => ((Person)source).Age)
-            .RecordValues(out var results);
-
-        // Act
-        person.Age = changedAge;
-
-        // Assert
-        results.Error.Should().BeNull(because: "supported reference casts must preserve property observation");
-        results.RecordedValues.Should().Equal(new[] { initialAge, changedAge }, because: "the runtime model remains the notification source");
-        results.HasCompleted.Should().BeFalse(because: "further age changes remain observable");
-    }
-
-    /// <summary>Verifies that an interface cast preserves observation after replacing an intermediate object.</summary>
-    [Fact]
-    public void InterfaceCastBeforePropertyAccess_ReplacementChildChanges_AreObserved()
-    {
-        // Arrange
-        var initialAge = _randomizer.Int(1, byte.MaxValue);
-        var replacementAge = initialAge + _randomizer.Int(1, byte.MaxValue);
-        var changedAge = replacementAge + _randomizer.Int(1, byte.MaxValue);
-        var parent = new ParentModel { Child = new ChildModel { Age = initialAge } };
-        var replacement = new ChildModel { Age = replacementAge };
-        using var subscription = parent.WhenValueChanged(static source => ((IHasAge)source.Child!).Age)
-            .RecordValues(out var results);
-        parent.Child = replacement;
-
-        // Act
-        replacement.Age = changedAge;
-
-        // Assert
-        results.Error.Should().BeNull(because: "supported interface casts must preserve nested property observation");
-        results.RecordedValues.Should().Equal(new[] { initialAge, replacementAge, changedAge },
-            because: "the interface property must follow the replacement child and its subsequent changes");
-        results.HasCompleted.Should().BeFalse(because: "further child changes remain observable");
-    }
-
-    /// <summary>Verifies that converted properties retain independent values and notification sources.</summary>
-    /// <param name="changeAmount">Whether to change the first observed property rather than the second.</param>
-    [Theory]
-    [InlineData(false)]
-    [InlineData(true)]
-    public void NumericConversionsOnDifferentProperties_Changes_AreIndependent(bool changeAmount)
-    {
-        // Arrange
-        var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
-        var initialOtherAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 8d;
-        var changedAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 16d;
-        var model = new ObservablePrice { Amount = initialAmount, OtherAmount = initialOtherAmount };
-        var initialScale = ((decimal)initialAmount).Scale;
-        var initialOtherScale = ((decimal)initialOtherAmount).Scale;
-        var changedScale = ((decimal)changedAmount).Scale;
-        var expectedScales = changeAmount ? new[] { initialScale, changedScale } : new[] { initialScale };
-        var expectedOtherScales = changeAmount ? new[] { initialOtherScale } : new[] { initialOtherScale, changedScale };
-        using var amountSubscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale)
-            .RecordValues(out var amounts);
-        using var otherSubscription = model.WhenValueChanged(static price => ((decimal)price.OtherAmount).Scale)
-            .RecordValues(out var otherAmounts);
-
-        // Act
-        if (changeAmount)
-        {
-            model.Amount = changedAmount;
-        }
-        else
-        {
-            model.OtherAmount = changedAmount;
-        }
-
-        // Assert
-        amounts.Error.Should().BeNull(because: "the first converted property remains observable");
-        otherAmounts.Error.Should().BeNull(because: "the second converted property remains observable");
-        amounts.RecordedValues.Should().Equal(expectedScales, because: "the first path observes only its own property");
-        otherAmounts.RecordedValues.Should().Equal(expectedOtherScales, because: "the second path observes only its own property");
-        amounts.HasCompleted.Should().BeFalse(because: "the first observation remains active");
-        otherAmounts.HasCompleted.Should().BeFalse(because: "the second observation remains active");
-    }
-
-    /// <summary>Verifies that different conversions of one property retain their own evaluation paths.</summary>
-    [Fact]
-    public void DifferentConversionPathsOnSameProperty_Changes_UseEachConversion()
-    {
-        // Arrange
-        var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
-        var changedAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 8d;
-        var model = new ObservablePrice { Amount = initialAmount };
-        var expectedScales = new[] { ((decimal)initialAmount).Scale, ((decimal)changedAmount).Scale };
-        var expectedTruncatedScales = new[] { ((decimal)(long)initialAmount).Scale, ((decimal)(long)changedAmount).Scale };
-        using var exactSubscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale)
-            .RecordValues(out var exact);
-        using var truncatedSubscription = model.WhenValueChanged(static price => ((decimal)(long)price.Amount).Scale)
-            .RecordValues(out var truncated);
-
-        // Act
-        model.Amount = changedAmount;
-
-        // Assert
-        exact.Error.Should().BeNull(because: "the direct conversion remains observable");
-        truncated.Error.Should().BeNull(because: "the conversion through an integer remains observable");
-        exact.RecordedValues.Should().Equal(expectedScales, because: "the direct path preserves fractional digits");
-        truncated.RecordedValues.Should().Equal(expectedTruncatedScales, because: "the integer conversion discards fractional digits");
-        exact.HasCompleted.Should().BeFalse(because: "the direct observation remains active");
-        truncated.HasCompleted.Should().BeFalse(because: "the integer-converted observation remains active");
-    }
-
-    /// <summary>Verifies that conversions to different result types do not share incompatible property factories.</summary>
-    [Fact]
-    public void LeafConversionsWithDifferentResultTypes_Changes_UseEachResultType()
-    {
-        // Arrange
-        var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
-        var changedAmount = initialAmount + _randomizer.Int(1, ushort.MaxValue);
-        var model = new ObservablePrice { Amount = initialAmount };
-        var expectedDecimals = new[] { (decimal)initialAmount, (decimal)changedAmount };
-        var expectedIntegers = new[] { (long)initialAmount, (long)changedAmount };
-        using var decimalSubscription = model.WhenValueChanged(static price => (decimal)price.Amount)
-            .RecordValues(out var decimals);
-        using var integerSubscription = model.WhenValueChanged(static price => (long)price.Amount)
-            .RecordValues(out var integers);
-
-        // Act
-        model.Amount = changedAmount;
-
-        // Assert
-        decimals.Error.Should().BeNull(because: "the decimal result must have a compatible factory");
-        integers.Error.Should().BeNull(because: "the integer result must have a compatible factory");
-        decimals.RecordedValues.Should().Equal(expectedDecimals, because: "the decimal path preserves fractional values");
-        integers.RecordedValues.Should().Equal(expectedIntegers, because: "the integer path truncates fractional values");
-        decimals.HasCompleted.Should().BeFalse(because: "the decimal observation remains active");
-        integers.HasCompleted.Should().BeFalse(because: "the integer observation remains active");
-    }
-
-    /// <summary>Verifies that conversion methods with matching source and result types retain distinct behavior.</summary>
-    [Fact]
-    public void ConversionMethodsWithSameSignature_Changes_UseEachMethod()
-    {
-        // Arrange
-        var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
-        var changedAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 8d;
-        var model = new ObservablePrice { Amount = initialAmount };
-        Func<double, decimal> exactConversion = ConvertAmount;
-        Func<double, decimal> truncatedConversion = TruncateAmount;
-        var parameter = Expression.Parameter(typeof(ObservablePrice), nameof(model));
-        var amount = Expression.Property(parameter, nameof(ObservablePrice.Amount));
-        var exactBody = Expression.Property(Expression.Convert(amount, typeof(decimal), exactConversion.Method), nameof(decimal.Scale));
-        var truncatedBody = Expression.Property(
-            Expression.Convert(amount, typeof(decimal), truncatedConversion.Method), nameof(decimal.Scale));
-        var exactPath = Expression.Lambda<Func<ObservablePrice, byte>>(exactBody, parameter);
-        var truncatedPath = Expression.Lambda<Func<ObservablePrice, byte>>(truncatedBody, parameter);
-        var expectedScales = new[] { exactConversion(initialAmount).Scale, exactConversion(changedAmount).Scale };
-        var expectedTruncatedScales = new[] { truncatedConversion(initialAmount).Scale, truncatedConversion(changedAmount).Scale };
-        using var exactSubscription = model.WhenValueChanged(exactPath)
-            .RecordValues(out var exact);
-        using var truncatedSubscription = model.WhenValueChanged(truncatedPath)
-            .RecordValues(out var truncated);
-
-        // Act
-        model.Amount = changedAmount;
-
-        // Assert
-        exact.Error.Should().BeNull(because: "the fractional conversion method remains observable");
-        truncated.Error.Should().BeNull(because: "the truncating conversion method remains observable");
-        exact.RecordedValues.Should().Equal(expectedScales, because: "the fractional conversion method belongs to this path");
-        truncated.RecordedValues.Should().Equal(expectedTruncatedScales, because: "the truncating conversion method belongs to this path");
-        exact.HasCompleted.Should().BeFalse(because: "the fractional observation remains active");
-        truncated.HasCompleted.Should().BeFalse(because: "the truncating observation remains active");
-    }
-
-    /// <summary>Verifies that a user-defined conversion operator is applied before reading a property of its result.</summary>
-    [Fact]
-    public void UserDefinedConversionBeforePropertyAccess_PropertyChanges_AreObserved()
-    {
-        // Arrange
-        // A fractional amount proves the operator ran, because it keeps only whole units.
-        var initialAmount = _randomizer.Int(1, ushort.MaxValue) + 0.5d;
-        var changedAmount = initialAmount + _randomizer.Int(1, ushort.MaxValue);
-        var model = new ObservablePrice { Amount = initialAmount };
-        var expectedUnits = new[] { ((Money)initialAmount).WholeUnits, ((Money)changedAmount).WholeUnits };
-        using var subscription = model.WhenValueChanged(static price => ((Money)price.Amount).WholeUnits)
-            .RecordValues(out var results);
-
-        // Act
-        model.Amount = changedAmount;
-
-        // Assert
-        results.Error.Should().BeNull(because: "a user-defined conversion operator must run before the next property is read");
-        results.RecordedValues.Should().Equal(expectedUnits, because: "each observed value must be read from the converted result");
-        results.HasCompleted.Should().BeFalse(because: "further amount changes remain observable");
-    }
-
-    /// <summary>Verifies that a user-defined conversion keeps its own evaluation path alongside a built-in conversion.</summary>
-    [Fact]
-    public void UserDefinedAndBuiltInConversionsOnSameProperty_Changes_UseEachConversion()
-    {
-        // Arrange
-        var initialAmount = _randomizer.Int(1, ushort.MaxValue) + 0.5d;
-        var changedAmount = initialAmount + _randomizer.Int(1, ushort.MaxValue);
-        var model = new ObservablePrice { Amount = initialAmount };
-        var expectedUnits = new[] { ((Money)initialAmount).WholeUnits, ((Money)changedAmount).WholeUnits };
-        var expectedScales = new[] { ((decimal)initialAmount).Scale, ((decimal)changedAmount).Scale };
-        using var moneySubscription = model.WhenValueChanged(static price => ((Money)price.Amount).WholeUnits)
-            .RecordValues(out var units);
-        using var decimalSubscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale)
-            .RecordValues(out var scales);
-
-        // Act
-        model.Amount = changedAmount;
-
-        // Assert
-        units.Error.Should().BeNull(because: "the user-defined conversion must have a compatible factory");
-        scales.Error.Should().BeNull(because: "the built-in conversion must have a compatible factory");
-        units.RecordedValues.Should().Equal(expectedUnits, because: "the user-defined path reports whole units");
-        scales.RecordedValues.Should().Equal(expectedScales, because: "the built-in path reports the decimal scale");
-        units.HasCompleted.Should().BeFalse(because: "the user-defined observation remains active");
-        scales.HasCompleted.Should().BeFalse(because: "the built-in observation remains active");
-    }
-
-    /// <summary>Verifies that equivalent converted paths share a factory regardless of lambda parameter names.</summary>
-    [Fact]
-    public void EquivalentConversionPaths_DifferentParameterNames_ReuseFactory()
-    {
-        // Arrange
-        Expression<Func<ObservablePrice, byte>> first = static price => ((decimal)price.Amount).Scale;
-        Expression<Func<ObservablePrice, byte>> second = static otherPrice => ((decimal)otherPrice.Amount).Scale;
-        var firstFactory = ObservablePropertyFactoryCache.Instance.GetFactory(first);
-
-        // Act
-        var secondFactory = ObservablePropertyFactoryCache.Instance.GetFactory(second);
-
-        // Assert
-        secondFactory.Should().BeSameAs(firstFactory, because: "parameter names do not change a property's evaluation path");
-    }
-
-    private static decimal ConvertAmount(double amount) => (decimal)amount;
-
-    private static decimal TruncateAmount(double amount) => decimal.Truncate((decimal)amount);
-
-    /// <summary>A conversion target reachable only through a user-defined conversion operator.</summary>
-    private sealed class Money
-    {
-        private Money(double amount) => WholeUnits = (int)amount;
-
-        /// <summary>Gets the whole units of the converted amount.</summary>
-        public int WholeUnits { get; }
-
-        public static explicit operator Money(double amount) => new(amount);
-    }
-}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedBehaviorFixture.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedBehaviorFixture.cs
deleted file mode 100644
index 863cbf110..000000000
--- a/src/DynamicData.Tests/Binding/WhenPropertyChangedBehaviorFixture.cs
+++ /dev/null
@@ -1,624 +0,0 @@
-// Copyright (c) 2011-2025 Roland Pheasant. All rights reserved.
-// Roland Pheasant licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for full license information.
-
-using System;
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Linq;
-using System.Reactive.Concurrency;
-using System.Reactive.Linq;
-
-using Bogus;
-
-using DynamicData.Binding;
-using DynamicData.Tests.Utilities;
-using FluentAssertions;
-
-using Xunit;
-using Xunit.Abstractions;
-
-namespace DynamicData.Tests.Binding;
-
-/// <summary>
-/// Single-threaded contract tests for <see cref="NotifyPropertyChangedEx.WhenPropertyChanged{TObject, TProperty}"/>:
-/// handler attachment ordering, subscription cleanup, expression conversions, no-dedup semantics, and deep-chain re-walks on swaps.
-/// </summary>
-public sealed partial class WhenPropertyChangedBehaviorFixture
-{
-    /// <summary>An arbitrary observed value; these tests assert handler lifetime, not the value itself.</summary>
-    private const double ObservedAmount = 41.375;
-
-    private readonly Randomizer _randomizer;
-
-    /// <summary>Initializes deterministic inputs for property-observation contracts.</summary>
-    /// <param name="output">Receives the seed used to generate test inputs.</param>
-    public WhenPropertyChangedBehaviorFixture(ITestOutputHelper output)
-    {
-        const int seed = 0x35C1_709B;
-        _randomizer = new Randomizer(seed);
-        output.WriteLine($"{nameof(WhenPropertyChangedBehaviorFixture)} seed: 0x{seed:X8}");
-    }
-
-    [Fact]
-    public void Shallow_NotifyInitialFalse_SubscribesHandlerBeforeReturning()
-    {
-        // notifyOnInitialValue=false: Subscribe must return only after the PropertyChanged handler
-        // is attached. A setter that fires immediately after Subscribe returns must reach the
-        // observer.
-        var model = new TestModel { Value = 10 };
-        var emissions = new List<int>();
-
-        using var sub = model.WhenPropertyChanged(m => m.Value, notifyOnInitialValue: false)
-            .Subscribe(pv => emissions.Add(pv.Value));
-
-        model.Value = 20;
-
-        emissions.Should().Equal(new[] { 20 });
-    }
-
-    [Fact]
-    public void Shallow_NotifyInitialTrue_DoesNotDedupSameValuedEvents()
-    {
-        var model = new TestModel { Value = 10 };
-        var emissions = new List<int>();
-
-        using var sub = model.WhenPropertyChanged(m => m.Value, notifyOnInitialValue: true)
-            .Subscribe(pv => emissions.Add(pv.Value));
-
-        model.Value = 10;
-        model.Value = 10;
-        model.Value = 10;
-
-        emissions.Should().Equal(new[] { 10, 10, 10, 10 });
-    }
-
-    [Fact]
-    public void Shallow_NotifyInitialFalse_DoesNotDedupSameValuedEvents()
-    {
-        var model = new TestModel { Value = 10 };
-        var emissions = new List<int>();
-
-        using var sub = model.WhenPropertyChanged(m => m.Value, notifyOnInitialValue: false)
-            .Subscribe(pv => emissions.Add(pv.Value));
-
-        model.Value = 42;
-        model.Value = 42;
-
-        emissions.Should().Equal(new[] { 42, 42 });
-    }
-
-    [Fact]
-    public void DeepChain_NotifyInitialTrue_DoesNotDedupSameValuedEvents()
-    {
-        var parent = new ParentModel { Child = new ChildModel { Age = 1 } };
-        var emissions = new List<int>();
-
-        using var sub = parent.WhenPropertyChanged(p => p.Child!.Age, notifyOnInitialValue: true)
-            .Subscribe(pv => emissions.Add(pv.Value));
-
-        parent.Child!.Age = 1;
-        parent.Child!.Age = 1;
-        parent.Child!.Age = 1;
-
-        emissions.Should().Equal(new[] { 1, 1, 1, 1 });
-    }
-
-    [Fact]
-    public void DeepChain_NotifyInitialFalse_DoesNotDedupSameValuedEvents()
-    {
-        var parent = new ParentModel { Child = new ChildModel { Age = 1 } };
-        var emissions = new List<int>();
-
-        using var sub = parent.WhenPropertyChanged(p => p.Child!.Age, notifyOnInitialValue: false)
-            .Subscribe(pv => emissions.Add(pv.Value));
-
-        parent.Child!.Age = 7;
-        parent.Child!.Age = 7;
-
-        emissions.Should().Equal(new[] { 7, 7 });
-    }
-
-    [Fact]
-    public void DeepChain_PostSwap_LeafEventOnNewChild_Captured()
-    {
-        // After parent.Child is reassigned, the leaf-level subscription must be re-attached
-        // against the new child. A subsequent leaf mutation on the new child must be captured.
-        var parent = new ParentModel { Child = new ChildModel { Age = 10 } };
-        var emissions = new List<int>();
-
-        using var sub = parent.WhenPropertyChanged(p => p.Child!.Age, notifyOnInitialValue: true)
-            .Subscribe(pv => emissions.Add(pv.Value));
-
-        var newChild = new ChildModel { Age = 20 };
-        parent.Child = newChild;
-        newChild.Age = 30;
-
-        emissions.Should().Equal(new[] { 10, 20, 30 });
-    }
-
-    [Fact]
-    public void DeepChain_MidChainSwap_DeeperLevelsRetargetCorrectly()
-    {
-        // Mid-chain swap on a 4-level chain. When level 3 is reassigned, the leaf subscription
-        // must re-attach against the new subtree; events on the old subtree must be ignored
-        // (its notifier subscription was disposed).
-        var l1 = new Level1
-        {
-            Child = new Level2
-            {
-                Child = new Level3
-                {
-                    Child = new Level4 { Leaf = 10 },
-                },
-            },
-        };
-
-        var emissions = new List<int>();
-        using var sub = l1.WhenPropertyChanged(x => x.Child!.Child!.Child!.Leaf, notifyOnInitialValue: true)
-            .Subscribe(pv => emissions.Add(pv.Value));
-
-        emissions.Should().Equal(new[] { 10 }, "initial emission");
-
-        var originalLeaf = l1.Child!.Child!.Child!;
-
-        var newL4 = new Level4 { Leaf = 20 };
-        l1.Child!.Child!.Child = newL4;
-
-        emissions.Should().Equal(new[] { 10, 20 }, "mid-chain swap emits the new leaf value");
-
-        newL4.Leaf = 30;
-        emissions.Should().Equal(new[] { 10, 20, 30 }, "leaf event on new subtree is captured");
-
-        originalLeaf.Leaf = 999;
-        emissions.Should().Equal(new[] { 10, 20, 30 }, "leaf event on detached subtree is ignored");
-    }
-
-    // https://github.com/reactivemarbles/DynamicData/issues/1149
-    [Fact]
-    public void ExpressionContainsImplicitInterfaceCast()
-    {
-        var child = new ChildModel()
-        {
-            Age = 10
-        };
-        
-        using var subscription = ObserveAge(child)
-            .RecordValues(out var results);
-
-        results.Error.Should().BeNull("no errors should have occurred");
-        results.RecordedValues.Should().ContainSingle("the initial value of the observed expression should have been published");
-        results.RecordedValues[0].Should().Be(child.Age, "the initial value of the observed expression should have been published");
-
-        ++child.Age;
-
-        results.Error.Should().BeNull("no errors should have occurred");
-        results.RecordedValues.Skip(1).Should().ContainSingle("the value of the observed expression changed once");
-        results.RecordedValues[1].Should().Be(child.Age, "the correct value should have been published");
-
-        static IObservable<int> ObserveAge<T>(T source)
-                where T : IHasAge
-            => source.WhenValueChanged(source => source.Age);
-    }
-
-    /// <summary>Verifies that a throwing initial observer leaves no property-change handler attached.</summary>
-    [Fact]
-    public void Shallow_InitialObserverThrows_DetachesHandler()
-    {
-        // Arrange
-        var model = new ObservablePrice { Amount = ObservedAmount };
-        var error = new InvalidOperationException();
-        var results = new ValueRecordingObserver<double>(ImmediateScheduler.Instance);
-        IObserver<double> observer = results;
-        var source = model.WhenValueChanged(static price => price.Amount);
-
-        // Act
-        Action subscribe = () =>
-        {
-            using var subscription = source.Subscribe(value =>
-            {
-                observer.OnNext(value);
-                throw error;
-            }, observer.OnError);
-        };
-
-        // Assert
-        subscribe.Should().Throw<InvalidOperationException>(because: "observer failures must escape Subscribe")
-            .Which.Should().BeSameAs(error, because: "the original observer failure must be preserved");
-        results.RecordedValues.Should().Equal(new[] { ObservedAmount }, because: "the failure occurs during initial delivery");
-        results.Error.Should().BeNull(because: "an observer failure must not be converted into an OnError notification");
-        model.WasSubscribed.Should().BeTrue(because: "registration must precede the initial value read");
-        model.HandlerCount.Should().Be(0, because: "a throwing Subscribe cannot return a disposable to its caller");
-    }
-
-    /// <summary>Verifies that a throwing initial observer releases property-change handlers at every chain level.</summary>
-    [Fact]
-    public void DeepChain_InitialObserverThrows_DetachesEveryHandler()
-    {
-        // Arrange
-        var leaf = new ObservablePrice { Amount = ObservedAmount };
-        var child = new ObservablePrice { Child = leaf };
-        var root = new ObservablePrice { Child = child };
-        var models = new[] { root, child, leaf };
-        var error = new InvalidOperationException();
-        var results = new ValueRecordingObserver<double>(ImmediateScheduler.Instance);
-        IObserver<double> observer = results;
-        var source = root.WhenValueChanged(static price => price.Child!.Child!.Amount);
-
-        // Act
-        Action subscribe = () =>
-        {
-            using var subscription = source.Subscribe(value =>
-            {
-                observer.OnNext(value);
-                throw error;
-            }, observer.OnError);
-        };
-
-        // Assert
-        subscribe.Should().Throw<InvalidOperationException>(because: "observer failures must escape Subscribe")
-            .Which.Should().BeSameAs(error, because: "the original observer failure must be preserved");
-        results.RecordedValues.Should().Equal(new[] { ObservedAmount }, because: "the failure occurs during initial delivery");
-        results.Error.Should().BeNull(because: "an observer failure must not be converted into an OnError notification");
-        models.Should().OnlyContain(model => model.WasSubscribed, because: "each observable level must be registered before it is read");
-        models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
-            because: "failed initialization must release every handler, not just the root handler");
-    }
-
-    /// <summary>Verifies that an initial getter failure releases the handler when the default error handler throws.</summary>
-    [Fact]
-    public void Shallow_InitialGetterThrows_DefaultErrorHandler_DetachesHandler()
-    {
-        // Arrange
-        var error = new InvalidOperationException();
-        var model = new ObservablePrice { Amount = ObservedAmount, ReadError = error };
-        var source = model.WhenValueChanged(static price => price.Amount);
-
-        // Act
-        Action subscribe = () =>
-        {
-            using var subscription = source.Subscribe();
-        };
-
-        // Assert
-        subscribe.Should().Throw<InvalidOperationException>(because: "the default Rx error handler must rethrow the getter failure")
-            .Which.Should().BeSameAs(error, because: "the original getter failure must be preserved");
-        model.WasSubscribed.Should().BeTrue(because: "registration must precede the initial value read");
-        model.HandlerCount.Should().Be(0, because: "failed initialization must not retain the event handler");
-    }
-
-    /// <summary>Verifies that a failing chain getter releases every handler when the default error handler throws.</summary>
-    /// <param name="notifyOnInitialValue">Whether subscribing requests an initial value notification.</param>
-    /// <param name="failBeforeLeaf">Whether an intermediate getter fails before the leaf can be subscribed.</param>
-    [Theory]
-    [InlineData(true, false)]
-    [InlineData(true, true)]
-    [InlineData(false, true)]
-    public void DeepChain_InitialGetterThrows_DefaultErrorHandler_DetachesEveryHandler(bool notifyOnInitialValue, bool failBeforeLeaf)
-    {
-        // Arrange
-        var error = new InvalidOperationException();
-        var leaf = new ObservablePrice { Amount = ObservedAmount, ReadError = failBeforeLeaf ? null : error };
-        var child = new ObservablePrice { Child = leaf, ChildReadError = failBeforeLeaf ? error : null };
-        var root = new ObservablePrice { Child = child };
-        var models = new[] { root, child, leaf };
-        var source = root.WhenValueChanged(static price => price.Child!.Child!.Amount, notifyOnInitialValue);
-
-        // Act
-        Action subscribe = () =>
-        {
-            using var subscription = source.Subscribe();
-        };
-
-        // Assert
-        subscribe.Should().Throw<Exception>(because: "the default Rx error handler must rethrow initialization failures")
-            .Which.GetBaseException().Should().BeSameAs(error, because: "the failure must originate in the observed getter");
-        root.WasSubscribed.Should().BeTrue(because: "the root handler must attach before its child is read");
-        child.WasSubscribed.Should().BeTrue(because: "the intermediate handler must attach before its child is read");
-        leaf.WasSubscribed.Should().Be(!failBeforeLeaf, because: "the leaf is reachable only if the intermediate getter succeeds");
-        models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
-            because: "failed initialization must release handlers at every visited level");
-    }
-
-    /// <summary>Verifies that a handled initial getter failure terminates observation and releases its event handler.</summary>
-    [Fact]
-    public void Shallow_InitialGetterThrows_ErrorIsRecordedAndHandlerDetached()
-    {
-        // Arrange
-        var error = new InvalidOperationException();
-        var model = new ObservablePrice { Amount = ObservedAmount, ReadError = error };
-
-        // Act
-        using var subscription = model.WhenPropertyChanged(static price => price.Amount)
-            .RecordValues(out var results);
-
-        // Assert
-        results.Error.Should().BeSameAs(error, because: "getter failures must be delivered through OnError");
-        results.RecordedValues.Should().BeEmpty(because: "the initial getter did not produce a value");
-        results.HasCompleted.Should().BeFalse(because: "OnError is the terminal notification");
-        model.WasSubscribed.Should().BeTrue(because: "registration must precede the initial value read");
-        model.HandlerCount.Should().Be(0, because: "OnError must release the handler before Subscribe returns");
-    }
-
-    /// <summary>Verifies that a handled chain getter failure terminates observation and releases every event handler.</summary>
-    /// <param name="notifyOnInitialValue">Whether subscribing requests an initial value notification.</param>
-    /// <param name="failBeforeLeaf">Whether an intermediate getter fails before the leaf can be subscribed.</param>
-    [Theory]
-    [InlineData(true, false)]
-    [InlineData(true, true)]
-    [InlineData(false, true)]
-    public void DeepChain_InitialGetterThrows_ErrorIsRecordedAndEveryHandlerDetached(bool notifyOnInitialValue, bool failBeforeLeaf)
-    {
-        // Arrange
-        var error = new InvalidOperationException();
-        var leaf = new ObservablePrice { Amount = ObservedAmount, ReadError = failBeforeLeaf ? null : error };
-        var child = new ObservablePrice { Child = leaf, ChildReadError = failBeforeLeaf ? error : null };
-        var root = new ObservablePrice { Child = child };
-        var models = new[] { root, child, leaf };
-
-        // Act
-        using var subscription = root.WhenPropertyChanged(static price => price.Child!.Child!.Amount, notifyOnInitialValue)
-            .RecordValues(out var results);
-
-        // Assert
-        results.Error.Should().NotBeNull(because: "chain getter failures must be delivered through OnError");
-        results.Error!.GetBaseException().Should().BeSameAs(error, because: "the failure must originate in the observed getter");
-        results.RecordedValues.Should().BeEmpty(because: "the chain did not produce an obtainable value");
-        results.HasCompleted.Should().BeFalse(because: "OnError is the terminal notification");
-        root.WasSubscribed.Should().BeTrue(because: "the root handler must attach before its child is read");
-        child.WasSubscribed.Should().BeTrue(because: "the intermediate handler must attach before its child is read");
-        leaf.WasSubscribed.Should().Be(!failBeforeLeaf, because: "the leaf is reachable only if the intermediate getter succeeds");
-        models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
-            because: "OnError must release every handler before Subscribe returns");
-    }
-
-    /// <summary>Verifies that live property handlers belong to the returned subscription until it is disposed.</summary>
-    /// <param name="deepChain">Whether the observed property is reached through intermediate objects.</param>
-    [Theory]
-    [InlineData(false)]
-    [InlineData(true)]
-    public void Subscription_ExplicitDisposal_ReleasesHandlers(bool deepChain)
-    {
-        // Arrange
-        var leaf = new ObservablePrice { Amount = ObservedAmount };
-        var child = new ObservablePrice { Child = leaf };
-        var root = new ObservablePrice { Child = child };
-        var models = deepChain ? new[] { root, child, leaf } : new[] { leaf };
-        var source = deepChain
-            ? root.WhenValueChanged(static price => price.Child!.Child!.Amount)
-            : leaf.WhenValueChanged(static price => price.Amount);
-        using var subscription = source.RecordValues(out var results);
-        var attachedHandlerCounts = models.Select(model => model.HandlerCount).ToArray();
-
-        // Act
-        subscription.Dispose();
-
-        // Assert
-        attachedHandlerCounts.Should().OnlyContain(count => count == 1, because: "each visited object must stay subscribed after initialization");
-        models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
-            because: "disposing the returned subscription must release every retained handler");
-        results.RecordedValues.Should().Equal(new[] { ObservedAmount }, because: "initialization must publish the observed value");
-        results.Error.Should().BeNull(because: "explicit disposal is not an observation failure");
-        results.HasCompleted.Should().BeFalse(because: "unsubscribing does not publish a completion notification");
-    }
-
-    /// <summary>Verifies that synchronous completion during initial delivery releases every property handler.</summary>
-    /// <param name="deepChain">Whether the observed property is reached through intermediate objects.</param>
-    [Theory]
-    [InlineData(false)]
-    [InlineData(true)]
-    public void Subscription_SynchronousCompletion_ReleasesHandlers(bool deepChain)
-    {
-        // Arrange
-        var leaf = new ObservablePrice { Amount = ObservedAmount };
-        var child = new ObservablePrice { Child = leaf };
-        var root = new ObservablePrice { Child = child };
-        var models = deepChain ? new[] { root, child, leaf } : new[] { leaf };
-        var source = deepChain
-            ? root.WhenValueChanged(static price => price.Child!.Child!.Amount)
-            : leaf.WhenValueChanged(static price => price.Amount);
-
-        // Act
-        using var subscription = source.Take(1)
-            .RecordValues(out var results);
-
-        // Assert
-        results.RecordedValues.Should().Equal(new[] { ObservedAmount }, because: "the requested initial value must be delivered");
-        results.Error.Should().BeNull(because: "taking an initial value is normal completion");
-        results.HasCompleted.Should().BeTrue(because: "Take completes after receiving its requested value");
-        models.Should().OnlyContain(model => model.WasSubscribed, because: "handlers must attach before initial delivery");
-        models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
-            because: "synchronous completion must release handlers before Subscribe returns");
-    }
-
-    /// <summary>
-    /// An observable input with numeric properties, whose custom event accessors expose property
-    /// subscription lifetimes and whose getters can be made to fail on demand.
-    /// </summary>
-    private sealed class ObservablePrice : INotifyPropertyChanged
-    {
-        private double _amount;
-        private ObservablePrice? _child;
-        private double _otherAmount;
-        private PropertyChangedEventHandler? _propertyChanged;
-
-        /// <inheritdoc />
-        public event PropertyChangedEventHandler? PropertyChanged
-        {
-            add
-            {
-                WasSubscribed = true;
-                _propertyChanged += value;
-            }
-
-            remove => _propertyChanged -= value;
-        }
-
-        /// <summary>Gets or sets the amount and raises a property-change notification when set.</summary>
-        public double Amount
-        {
-            get => ReadError is null ? _amount : throw ReadError;
-            set
-            {
-                _amount = value;
-                _propertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Amount)));
-            }
-        }
-
-        /// <summary>Gets the next object in a nested property path.</summary>
-        public ObservablePrice? Child
-        {
-            get => ChildReadError is null ? _child : throw ChildReadError;
-            init => _child = value;
-        }
-
-        /// <summary>Gets an optional failure raised when reading <see cref="Child"/>.</summary>
-        public InvalidOperationException? ChildReadError { get; init; }
-
-        /// <summary>Gets the number of event handlers retained by this object.</summary>
-        public int HandlerCount => _propertyChanged?.GetInvocationList().Length ?? 0;
-
-        /// <summary>Gets an optional failure raised when reading <see cref="Amount"/>.</summary>
-        public InvalidOperationException? ReadError { get; init; }
-
-        /// <summary>Gets or sets a second amount, used to observe two converted paths on one object.</summary>
-        public double OtherAmount
-        {
-            get => _otherAmount;
-            set
-            {
-                _otherAmount = value;
-                _propertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(OtherAmount)));
-            }
-        }
-
-        /// <summary>Gets whether any observer has registered a property-change handler.</summary>
-        public bool WasSubscribed { get; private set; }
-    }
-    
-    private interface IHasAge
-        : INotifyPropertyChanged
-    {
-        int Age { get; }
-    }
-
-    private sealed class TestModel : INotifyPropertyChanged
-    {
-        private int _value;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public int Value
-        {
-            get => _value;
-            set
-            {
-                _value = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Value)));
-            }
-        }
-    }
-
-    private sealed class ParentModel : INotifyPropertyChanged
-    {
-        private ChildModel? _child;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public ChildModel? Child
-        {
-            get => _child;
-            set
-            {
-                _child = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
-            }
-        }
-    }
-
-    private sealed class ChildModel
-        : IHasAge
-    {
-        private int _age;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public int Age
-        {
-            get => _age;
-            set
-            {
-                _age = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Age)));
-            }
-        }
-    }
-
-    private sealed class Level1 : INotifyPropertyChanged
-    {
-        private Level2? _child;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public Level2? Child
-        {
-            get => _child;
-            set
-            {
-                _child = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
-            }
-        }
-    }
-
-    private sealed class Level2 : INotifyPropertyChanged
-    {
-        private Level3? _child;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public Level3? Child
-        {
-            get => _child;
-            set
-            {
-                _child = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
-            }
-        }
-    }
-
-    private sealed class Level3 : INotifyPropertyChanged
-    {
-        private Level4? _child;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public Level4? Child
-        {
-            get => _child;
-            set
-            {
-                _child = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
-            }
-        }
-    }
-
-    private sealed class Level4 : INotifyPropertyChanged
-    {
-        private int _leaf;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public int Leaf
-        {
-            get => _leaf;
-            set
-            {
-                _leaf = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Leaf)));
-            }
-        }
-    }
-}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.IntegrationTests.DeepChain.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.IntegrationTests.DeepChain.cs
new file mode 100644
index 000000000..eb6b35173
--- /dev/null
+++ b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.IntegrationTests.DeepChain.cs
@@ -0,0 +1,218 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using System.Reactive;
+
+using Bogus;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Binding;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Binding;
+ 
+public static partial class WhenPropertyChangedFixture
+{
+    public partial class IntegrationTests
+    {
+        [Fact]
+        public async Task DeepChain_ConcurrentLeafMutationDuringInitialEmit_NotDropped()
+        {
+            // Deep-chain version of the above. The observer blocks inside its OnNext for the initial
+            // leaf value while a second thread mutates the leaf.
+            var parent = new ParentModel { Child = new ChildModel { Age = 10 } };
+
+            var whenSubscribing = new ManualResetEventSlim();
+            var whenValueChanged = new ManualResetEventSlim();
+
+            var emissions = new List<int>();
+            var observer = Observer.Create<PropertyValue<ParentModel, int>>(pv =>
+            {
+                emissions.Add(pv.Value);
+                whenSubscribing.Set();
+                whenValueChanged.Wait();
+            });
+
+            var source = parent.WhenPropertyChanged(static p => p.Child!.Age, notifyOnInitialValue: true);
+
+            await Task.WhenAll(
+                Task.Run(() =>
+                {
+                    using var subscription = source.Subscribe(observer);
+                }),
+                Task.Run(() =>
+                {
+                    whenSubscribing.Wait();
+                    parent.Child!.Age = 20;
+                    whenValueChanged.Set();
+                })).WaitAsync(ConditionTimeout);
+
+            emissions.Should().Equal(new[] { 10, 20 });
+        }
+
+        [Fact]
+        public async Task DeepChain_ConcurrentParentSwap_LeafEventOnWinnerNotDropped()
+        {
+            // Two threads concurrently swap parent.Child. After both swaps complete, a leaf mutation
+            // on the current child must be captured. SharedDeliveryQueue serialises the level-0
+            // signals on the drainer, so the final level-1 subscription always targets parent.Child's
+            // current value.
+            const int iterations = 50;
+            var losses = 0;
+
+            for (var iter = 0; iter < iterations; iter++)
+            {
+                var parent = new ParentModel { Child = new ChildModel { Age = 0 } };
+                var emissions = new List<int>();
+
+                using var sub = parent.WhenPropertyChanged(p => p.Child!.Age, notifyOnInitialValue: false)
+                    .Subscribe(pv => { lock (emissions) emissions.Add(pv.Value); });
+
+                var newChild1 = new ChildModel { Age = 1 };
+                var newChild2 = new ChildModel { Age = 2 };
+
+                using var barrier = new Barrier(2);
+                var taskA = Task.Run(() => { barrier.SignalAndWait(); parent.Child = newChild1; });
+                var taskB = Task.Run(() => { barrier.SignalAndWait(); parent.Child = newChild2; });
+                await Task.WhenAll(taskA, taskB).WaitAsync(ConditionTimeout);
+
+                var winner = parent.Child;
+                if (winner is null)
+                {
+                    continue;
+                }
+
+                winner.Age = 99;
+
+                WaitForCondition(() => { lock (emissions) return emissions.Contains(99); });
+
+                lock (emissions)
+                {
+                    if (!emissions.Contains(99))
+                    {
+                        losses++;
+                    }
+                }
+            }
+
+            losses.Should().Be(0, $"out of {iterations} iterations, {losses} dropped the leaf event on the post-swap winner");
+        }
+
+        [Fact]
+        public async Task DeepChain_FiveLevels_AllLevelsMutatedConcurrently_FinalEmissionMatchesActual()
+        {
+            // Torture: five worker threads each mutating at a different level of a 5-level chain.
+            // Mutations that land on detached subtrees are ignored (their notifier subscriptions were
+            // disposed by ResubscribeFrom). Mutations on the live chain reach the drainer.
+            //
+            // Three invariants per iteration:
+            //   (a) Rx contract: ValidateSynchronization catches any concurrent OnNext on the user
+            //       observer (a SharedDeliveryQueue serialisation failure).
+            //   (b) Value legality: every emission must be a value that some thread legitimately
+            //       wrote.
+            //   (c) Final consistency: after Task.WhenAll the drainer continues until the queue is
+            //       empty. The last processed signal triggers a ReadCurrent against the now-frozen
+            //       chain state, so emissions.Last() == ReadCurrent().
+            const int iterations = 50;
+            const int mutationsPerThread = 200;
+            var mismatches = 0;
+
+            for (var iter = 0; iter < iterations; iter++)
+            {
+                var root = NewDeepChain(0);
+                var emissions = new List<int>();
+
+                using var sub = root.WhenPropertyChanged(r => r.Child!.Child!.Child!.Child!.Leaf, notifyOnInitialValue: true)
+                    .ValidateSynchronization()
+                    .Subscribe(pv => { lock (emissions) emissions.Add(pv.Value); });
+
+                using var barrier = new Barrier(5);
+                var iterSeed = iter * 10_000;
+                var tasks = new[]
+                {
+                    Task.Run(() =>
+                    {
+                        barrier.SignalAndWait();
+                        for (var i = 0; i < mutationsPerThread; i++)
+                        {
+                            root.Child = NewDeep2(iterSeed + 40_000 + i);
+                        }
+                    }),
+                    Task.Run(() =>
+                    {
+                        barrier.SignalAndWait();
+                        for (var i = 0; i < mutationsPerThread; i++)
+                        {
+                            var l2 = root.Child;
+                            if (l2 is not null) l2.Child = NewDeep3(iterSeed + 30_000 + i);
+                        }
+                    }),
+                    Task.Run(() =>
+                    {
+                        barrier.SignalAndWait();
+                        for (var i = 0; i < mutationsPerThread; i++)
+                        {
+                            var l3 = root.Child?.Child;
+                            if (l3 is not null) l3.Child = NewDeep4(iterSeed + 20_000 + i);
+                        }
+                    }),
+                    Task.Run(() =>
+                    {
+                        barrier.SignalAndWait();
+                        for (var i = 0; i < mutationsPerThread; i++)
+                        {
+                            var l4 = root.Child?.Child?.Child;
+                            if (l4 is not null) l4.Child = new Deep5 { Leaf = iterSeed + 10_000 + i };
+                        }
+                    }),
+                    Task.Run(() =>
+                    {
+                        barrier.SignalAndWait();
+                        for (var i = 0; i < mutationsPerThread; i++)
+                        {
+                            var l5 = root.Child?.Child?.Child?.Child;
+                            if (l5 is not null) l5.Leaf = i;
+                        }
+                    }),
+                };
+
+                await Task.WhenAll(tasks).WaitAsync(ConditionTimeout);
+
+                var actualFinal = root.Child!.Child!.Child!.Child!.Leaf;
+
+                WaitForCondition(() => { lock (emissions) return emissions.Count > 0 && emissions[^1] == actualFinal; });
+
+                var legal = new HashSet<int> { 0 };
+                for (var i = 0; i < mutationsPerThread; i++)
+                {
+                    legal.Add(i);
+                    legal.Add(iterSeed + 10_000 + i);
+                    legal.Add(iterSeed + 20_000 + i);
+                    legal.Add(iterSeed + 30_000 + i);
+                    legal.Add(iterSeed + 40_000 + i);
+                }
+
+                lock (emissions)
+                {
+                    emissions.Should().NotBeEmpty($"iter {iter}: notifyOnInitialValue=true requires at least the initial emission");
+                    emissions[0].Should().Be(0, $"iter {iter}: first emission must be the initial value");
+
+                    var illegal = emissions.Where(v => !legal.Contains(v)).ToList();
+                    illegal.Should().BeEmpty($"iter {iter}: every emission must be a value some thread wrote; saw {string.Join(",", illegal.Take(5))}");
+
+                    if (emissions.Count == 0 || emissions[^1] != actualFinal)
+                    {
+                        mismatches++;
+                    }
+                }
+            }
+
+            mismatches.Should().Be(0, $"out of {iterations} iterations, {mismatches} ended with the last emission not matching the actual final chain leaf");
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.IntegrationTests.Shallow.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.IntegrationTests.Shallow.cs
new file mode 100644
index 000000000..0545fdb8b
--- /dev/null
+++ b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.IntegrationTests.Shallow.cs
@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using System.Reactive;
+
+using Bogus;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Binding;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Binding;
+ 
+public static partial class WhenPropertyChangedFixture
+{
+    public partial class IntegrationTests
+    {
+        [Fact]
+        public async Task Shallow_ConcurrentMutationDuringInitialEmit_NotDropped()
+        {
+            var item = new Item()
+            {
+                Id = 1,
+                Value = 10
+            };
+
+            var whenSubscribing = new ManualResetEventSlim();
+            var whenValueChanged = new ManualResetEventSlim();
+
+            var source = item.WhenPropertyChanged(
+                propertyAccessor:       static item => item.Value,
+                notifyOnInitialValue:   true);
+
+            var observedValues = new List<int>();
+            var observer = Observer.Create<PropertyValue<Item, int>>(propertyValue =>
+            {
+                observedValues.Add(propertyValue.Value);
+
+                whenSubscribing.Set();
+                whenValueChanged.Wait();
+            });
+
+            await Task.WhenAll(
+                Task.Run(() =>
+                {
+                    using var subscription = source.Subscribe(observer);
+                }),
+                Task.Run(() =>
+                {
+                    whenSubscribing.Wait();
+
+                    item.Value = 20;
+
+                    whenValueChanged.Set();
+                }));
+
+            observedValues.Should().BeEquivalentTo(
+                expectation:    new [] { 10, 20 },
+                config:         options => options.WithStrictOrdering(),
+                because:        "All change events occurring after publication of the initial value should be captured and forwarded.");
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.IntegrationTests.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.IntegrationTests.cs
new file mode 100644
index 000000000..56e2acfd2
--- /dev/null
+++ b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.IntegrationTests.cs
@@ -0,0 +1,129 @@
+using System;
+using System.Linq;
+using System.Reactive.Concurrency;
+using System.Reactive.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+using FluentAssertions;
+
+using Xunit;
+
+namespace DynamicData.Tests.Binding;
+ 
+public static partial class WhenPropertyChangedFixture
+{
+    public sealed partial class IntegrationTests
+        : IntegrationTestFixtureBase
+    {
+        private static readonly TimeSpan ConditionTimeout
+            = TimeSpan.FromSeconds(30);
+
+        private static void WaitForCondition(Func<bool> condition, TimeSpan? timeout = null) =>
+            SpinWait.SpinUntil(condition, timeout ?? ConditionTimeout);
+
+        [Fact(Skip = "AutoRefresh has a separate concurrency bug; tracked separately")]
+        public async Task AutoRefreshThenFilter_ConcurrentAddsAndPropertyActivation_AllItemsObserved()
+        {
+            // One adder thread sequentially adds items to the cache while a single flipper thread
+            // concurrently sets each item's Activated to true. Final filter contents must include
+            // every item (every item ends Activated=true).
+            //
+            // KeyedActivable's setter only raises PropertyChanged on actual value change, so a
+            // dropped false->true transition is unrecoverable.
+            //
+            // The race lives in AutoRefresh's internal Publish multicast: Sub 1 (Filter path)
+            // receives the Add and reads the property before Sub 2 (MergeMany) subscribes the
+            // per-item refresh handler. A concurrent flip landing in that gap is dropped. This
+            // is not a WhenPropertyChanged issue: AutoRefresh calls WhenPropertyChanged with
+            // notifyInitial=false, so the per-item subscribe attaches the handler immediately
+            // and has no internal race window.
+            const int iterations = 100;
+            const int itemCount = 200;
+
+            for (var iter = 0; iter < iterations; iter++)
+            {
+                using var cache = new SourceCache<KeyedActivable, int>(x => x.Id);
+                var items = Enumerable.Range(0, itemCount).Select(i => new KeyedActivable(i)).ToList();
+
+                using var results = cache.Connect()
+                    .AutoRefresh(x => x.Activated)
+                    .Filter(x => x.Activated)
+                    .AsAggregator();
+
+                using var barrier = new Barrier(2);
+
+                var adder = Task.Run(() =>
+                {
+                    barrier.SignalAndWait();
+                    foreach (var item in items) cache.AddOrUpdate(item);
+                });
+
+                var flipper = Task.Run(() =>
+                {
+                    barrier.SignalAndWait();
+                    foreach (var item in items) item.Activated = true;
+                });
+
+                await Task.WhenAll(adder, flipper).WaitAsync(ConditionTimeout);
+
+                var expected = items.Select(x => x.Id).ToHashSet();
+                WaitForCondition(() => results.Data.Keys.ToHashSet().SetEquals(expected));
+
+                var actual = results.Data.Keys.ToHashSet();
+                actual.Should().BeEquivalentTo(expected, $"iter {iter}: every item ends Activated=true and must appear in the filter (missing: {string.Join(",", expected.Except(actual))})");
+                results.Error.Should().BeNull($"iter {iter}: pipeline must not error");
+            }
+        }
+
+        [Fact(Skip = "AutoRefresh has a separate concurrency bug; tracked separately")]
+        public async Task AutoRefreshThenFilter_DualSubscribers_AllItemsObserved()
+        {
+            // Two independent cache subscribers running on the ThreadPool:
+            //   Sub 1 (mutator): on every Add change, flips item.Activated to true
+            //   Sub 2 (filter chain): AutoRefresh + Filter (filter = Activated)
+            // Items start with Activated=false (filtered out). The mutator flips every item, so
+            // the final filter contents must include every item.
+            //
+            // Same root cause as the single-flipper variant above: AutoRefresh's internal Publish
+            // multicasts the Add to the Filter path before MergeMany subscribes the per-item
+            // refresh handler. The mutator's flip can land in that gap and be dropped.
+            const int iterations = 100;
+            const int itemCount = 200;
+
+            for (var iter = 0; iter < iterations; iter++)
+            {
+                using var cache = new SourceCache<KeyedActivable, int>(x => x.Id);
+                var items = Enumerable.Range(0, itemCount).Select(i => new KeyedActivable(i)).ToList();
+
+                using var mutator = cache.Connect()
+                    .ObserveOn(TaskPoolScheduler.Default)
+                    .Subscribe(changes =>
+                    {
+                        foreach (var change in changes)
+                        {
+                            if (change.Reason == ChangeReason.Add)
+                            {
+                                change.Current.Activated = true;
+                            }
+                        }
+                    });
+
+                using var results = cache.Connect()
+                    .ObserveOn(TaskPoolScheduler.Default)
+                    .AutoRefresh(x => x.Activated)
+                    .Filter(x => x.Activated)
+                    .AsAggregator();
+
+                foreach (var item in items) cache.AddOrUpdate(item);
+
+                var expected = items.Select(x => x.Id).ToHashSet();
+                WaitForCondition(() => results.Data.Keys.ToHashSet().SetEquals(expected));
+
+                var actual = results.Data.Keys.ToHashSet();
+                actual.Should().BeEquivalentTo(expected, $"iter {iter}: every item was flipped to Activated=true by the mutator and must appear in the filter (missing: {string.Join(",", expected.Except(actual))})");
+                results.Error.Should().BeNull($"iter {iter}: pipeline must not error");
+            }
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.Conversions.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.Conversions.cs
new file mode 100644
index 000000000..a18655e0c
--- /dev/null
+++ b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.Conversions.cs
@@ -0,0 +1,327 @@
+using System;
+using System.ComponentModel;
+using System.Linq.Expressions;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Binding;
+using DynamicData.Tests.Domain;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Binding;
+
+public static partial class WhenPropertyChangedFixture
+{
+    public partial class UnitTests
+    {
+        [Fact]
+        public void NumericConversionBeforePropertyAccess_InitialValue_IsObserved()
+        {
+            // Arrange
+            // An odd numerator produces an exactly representable, non-integral amount.
+            var amount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
+            var model = new ObservablePrice { Amount = amount };
+            var expectedScale = ((decimal)amount).Scale;
+
+            // Act
+            using var subscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale)
+                .RecordValues(out var results);
+
+            // Assert
+            results.Error.Should().BeNull(because: "the next property belongs to the converted decimal, not the source double");
+            results.RecordedValues.Should().Equal(new[] { expectedScale }, because: "the initial value must match the supplied expression");
+            results.HasCompleted.Should().BeFalse(because: "further amount changes remain observable");
+        }
+
+        /// <summary>Verifies that property changes remain observable through a value-changing numeric conversion.</summary>
+        /// <param name="notifyOnInitialValue">Whether subscribing requests an initial value notification.</param>
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public void NumericConversionBeforePropertyAccess_PropertyChanges_AreObserved(bool notifyOnInitialValue)
+        {
+            // Arrange
+            // Odd quarters and eighths have distinct decimal scales without floating-point rounding.
+            var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
+            var changedAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 8d;
+            var model = new ObservablePrice { Amount = initialAmount };
+            var initialScale = ((decimal)initialAmount).Scale;
+            var changedScale = ((decimal)changedAmount).Scale;
+            var expectedScales = notifyOnInitialValue ? new[] { initialScale, changedScale } : new[] { changedScale };
+            using var subscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale, notifyOnInitialValue)
+                .RecordValues(out var results);
+
+            // Act
+            model.Amount = changedAmount;
+
+            // Assert
+            results.Error.Should().BeNull(because: "conversion must be applied on both initial and subsequent chain reads");
+            results.RecordedValues.Should().Equal(expectedScales, because: "notifications must match the expression and initial-value option");
+            results.HasCompleted.Should().BeFalse(because: "amount changes do not complete the observation");
+        }
+
+        /// <summary>Verifies that a numeric conversion at the end of a property path preserves initial and changed values.</summary>
+        [Fact]
+        public void NumericConversionAtLeaf_PropertyChanges_AreObserved()
+        {
+            // Arrange
+            var initialAmount = _randomizer.Double();
+            var changedAmount = initialAmount + _randomizer.Double(1, 2);
+            var model = new ObservablePrice { Amount = initialAmount };
+            var expectedAmounts = new[] { (decimal)initialAmount, (decimal)changedAmount };
+            using var subscription = model.WhenValueChanged(static price => (decimal)price.Amount)
+                .RecordValues(out var results);
+
+            // Act
+            model.Amount = changedAmount;
+
+            // Assert
+            results.Error.Should().BeNull(because: "a conversion must also remain supported as the final expression step");
+            results.RecordedValues.Should().Equal(expectedAmounts, because: "each observed value must be converted to the requested type");
+            results.HasCompleted.Should().BeFalse(because: "further amount changes remain observable");
+        }
+
+        /// <summary>Verifies that a reference cast preserves observation of properties on the runtime model.</summary>
+        [Fact]
+        public void ReferenceCastBeforePropertyAccess_PropertyChanges_AreObserved()
+        {
+            // Arrange
+            var person = Fakers.Person.Clone().WithSeed(_randomizer).Generate();
+            INotifyPropertyChanged model = person;
+            var initialAge = person.Age;
+            var changedAge = initialAge + _randomizer.Int(1, byte.MaxValue);
+            using var subscription = model.WhenValueChanged(static source => ((Person)source).Age)
+                .RecordValues(out var results);
+
+            // Act
+            person.Age = changedAge;
+
+            // Assert
+            results.Error.Should().BeNull(because: "supported reference casts must preserve property observation");
+            results.RecordedValues.Should().Equal(new[] { initialAge, changedAge }, because: "the runtime model remains the notification source");
+            results.HasCompleted.Should().BeFalse(because: "further age changes remain observable");
+        }
+
+        /// <summary>Verifies that an interface cast preserves observation after replacing an intermediate object.</summary>
+        [Fact]
+        public void InterfaceCastBeforePropertyAccess_ReplacementChildChanges_AreObserved()
+        {
+            // Arrange
+            var initialAge = _randomizer.Int(1, byte.MaxValue);
+            var replacementAge = initialAge + _randomizer.Int(1, byte.MaxValue);
+            var changedAge = replacementAge + _randomizer.Int(1, byte.MaxValue);
+            var parent = new ParentModel { Child = new ChildModel { Age = initialAge } };
+            var replacement = new ChildModel { Age = replacementAge };
+            using var subscription = parent.WhenValueChanged(static source => ((IHasAge)source.Child!).Age)
+                .RecordValues(out var results);
+            parent.Child = replacement;
+
+            // Act
+            replacement.Age = changedAge;
+
+            // Assert
+            results.Error.Should().BeNull(because: "supported interface casts must preserve nested property observation");
+            results.RecordedValues.Should().Equal(new[] { initialAge, replacementAge, changedAge },
+                because: "the interface property must follow the replacement child and its subsequent changes");
+            results.HasCompleted.Should().BeFalse(because: "further child changes remain observable");
+        }
+
+        /// <summary>Verifies that converted properties retain independent values and notification sources.</summary>
+        /// <param name="changeAmount">Whether to change the first observed property rather than the second.</param>
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public void NumericConversionsOnDifferentProperties_Changes_AreIndependent(bool changeAmount)
+        {
+            // Arrange
+            var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
+            var initialOtherAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 8d;
+            var changedAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 16d;
+            var model = new ObservablePrice { Amount = initialAmount, OtherAmount = initialOtherAmount };
+            var initialScale = ((decimal)initialAmount).Scale;
+            var initialOtherScale = ((decimal)initialOtherAmount).Scale;
+            var changedScale = ((decimal)changedAmount).Scale;
+            var expectedScales = changeAmount ? new[] { initialScale, changedScale } : new[] { initialScale };
+            var expectedOtherScales = changeAmount ? new[] { initialOtherScale } : new[] { initialOtherScale, changedScale };
+            using var amountSubscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale)
+                .RecordValues(out var amounts);
+            using var otherSubscription = model.WhenValueChanged(static price => ((decimal)price.OtherAmount).Scale)
+                .RecordValues(out var otherAmounts);
+
+            // Act
+            if (changeAmount)
+            {
+                model.Amount = changedAmount;
+            }
+            else
+            {
+                model.OtherAmount = changedAmount;
+            }
+
+            // Assert
+            amounts.Error.Should().BeNull(because: "the first converted property remains observable");
+            otherAmounts.Error.Should().BeNull(because: "the second converted property remains observable");
+            amounts.RecordedValues.Should().Equal(expectedScales, because: "the first path observes only its own property");
+            otherAmounts.RecordedValues.Should().Equal(expectedOtherScales, because: "the second path observes only its own property");
+            amounts.HasCompleted.Should().BeFalse(because: "the first observation remains active");
+            otherAmounts.HasCompleted.Should().BeFalse(because: "the second observation remains active");
+        }
+
+        /// <summary>Verifies that different conversions of one property retain their own evaluation paths.</summary>
+        [Fact]
+        public void DifferentConversionPathsOnSameProperty_Changes_UseEachConversion()
+        {
+            // Arrange
+            var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
+            var changedAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 8d;
+            var model = new ObservablePrice { Amount = initialAmount };
+            var expectedScales = new[] { ((decimal)initialAmount).Scale, ((decimal)changedAmount).Scale };
+            var expectedTruncatedScales = new[] { ((decimal)(long)initialAmount).Scale, ((decimal)(long)changedAmount).Scale };
+            using var exactSubscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale)
+                .RecordValues(out var exact);
+            using var truncatedSubscription = model.WhenValueChanged(static price => ((decimal)(long)price.Amount).Scale)
+                .RecordValues(out var truncated);
+
+            // Act
+            model.Amount = changedAmount;
+
+            // Assert
+            exact.Error.Should().BeNull(because: "the direct conversion remains observable");
+            truncated.Error.Should().BeNull(because: "the conversion through an integer remains observable");
+            exact.RecordedValues.Should().Equal(expectedScales, because: "the direct path preserves fractional digits");
+            truncated.RecordedValues.Should().Equal(expectedTruncatedScales, because: "the integer conversion discards fractional digits");
+            exact.HasCompleted.Should().BeFalse(because: "the direct observation remains active");
+            truncated.HasCompleted.Should().BeFalse(because: "the integer-converted observation remains active");
+        }
+
+        /// <summary>Verifies that conversions to different result types do not share incompatible property factories.</summary>
+        [Fact]
+        public void LeafConversionsWithDifferentResultTypes_Changes_UseEachResultType()
+        {
+            // Arrange
+            var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
+            var changedAmount = initialAmount + _randomizer.Int(1, ushort.MaxValue);
+            var model = new ObservablePrice { Amount = initialAmount };
+            var expectedDecimals = new[] { (decimal)initialAmount, (decimal)changedAmount };
+            var expectedIntegers = new[] { (long)initialAmount, (long)changedAmount };
+            using var decimalSubscription = model.WhenValueChanged(static price => (decimal)price.Amount)
+                .RecordValues(out var decimals);
+            using var integerSubscription = model.WhenValueChanged(static price => (long)price.Amount)
+                .RecordValues(out var integers);
+
+            // Act
+            model.Amount = changedAmount;
+
+            // Assert
+            decimals.Error.Should().BeNull(because: "the decimal result must have a compatible factory");
+            integers.Error.Should().BeNull(because: "the integer result must have a compatible factory");
+            decimals.RecordedValues.Should().Equal(expectedDecimals, because: "the decimal path preserves fractional values");
+            integers.RecordedValues.Should().Equal(expectedIntegers, because: "the integer path truncates fractional values");
+            decimals.HasCompleted.Should().BeFalse(because: "the decimal observation remains active");
+            integers.HasCompleted.Should().BeFalse(because: "the integer observation remains active");
+        }
+
+        /// <summary>Verifies that conversion methods with matching source and result types retain distinct behavior.</summary>
+        [Fact]
+        public void ConversionMethodsWithSameSignature_Changes_UseEachMethod()
+        {
+            // Arrange
+            var initialAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 4d;
+            var changedAmount = (_randomizer.Int(1, ushort.MaxValue) | 1) / 8d;
+            var model = new ObservablePrice { Amount = initialAmount };
+            Func<double, decimal> exactConversion = ConvertAmount;
+            Func<double, decimal> truncatedConversion = TruncateAmount;
+            var parameter = Expression.Parameter(typeof(ObservablePrice), nameof(model));
+            var amount = Expression.Property(parameter, nameof(ObservablePrice.Amount));
+            var exactBody = Expression.Property(Expression.Convert(amount, typeof(decimal), exactConversion.Method), nameof(decimal.Scale));
+            var truncatedBody = Expression.Property(
+                Expression.Convert(amount, typeof(decimal), truncatedConversion.Method), nameof(decimal.Scale));
+            var exactPath = Expression.Lambda<Func<ObservablePrice, byte>>(exactBody, parameter);
+            var truncatedPath = Expression.Lambda<Func<ObservablePrice, byte>>(truncatedBody, parameter);
+            var expectedScales = new[] { exactConversion(initialAmount).Scale, exactConversion(changedAmount).Scale };
+            var expectedTruncatedScales = new[] { truncatedConversion(initialAmount).Scale, truncatedConversion(changedAmount).Scale };
+            using var exactSubscription = model.WhenValueChanged(exactPath)
+                .RecordValues(out var exact);
+            using var truncatedSubscription = model.WhenValueChanged(truncatedPath)
+                .RecordValues(out var truncated);
+
+            // Act
+            model.Amount = changedAmount;
+
+            // Assert
+            exact.Error.Should().BeNull(because: "the fractional conversion method remains observable");
+            truncated.Error.Should().BeNull(because: "the truncating conversion method remains observable");
+            exact.RecordedValues.Should().Equal(expectedScales, because: "the fractional conversion method belongs to this path");
+            truncated.RecordedValues.Should().Equal(expectedTruncatedScales, because: "the truncating conversion method belongs to this path");
+            exact.HasCompleted.Should().BeFalse(because: "the fractional observation remains active");
+            truncated.HasCompleted.Should().BeFalse(because: "the truncating observation remains active");
+        }
+
+        /// <summary>Verifies that a user-defined conversion operator is applied before reading a property of its result.</summary>
+        [Fact]
+        public void UserDefinedConversionBeforePropertyAccess_PropertyChanges_AreObserved()
+        {
+            // Arrange
+            // A fractional amount proves the operator ran, because it keeps only whole units.
+            var initialAmount = _randomizer.Int(1, ushort.MaxValue) + 0.5d;
+            var changedAmount = initialAmount + _randomizer.Int(1, ushort.MaxValue);
+            var model = new ObservablePrice { Amount = initialAmount };
+            var expectedUnits = new[] { ((Money)initialAmount).WholeUnits, ((Money)changedAmount).WholeUnits };
+            using var subscription = model.WhenValueChanged(static price => ((Money)price.Amount).WholeUnits)
+                .RecordValues(out var results);
+
+            // Act
+            model.Amount = changedAmount;
+
+            // Assert
+            results.Error.Should().BeNull(because: "a user-defined conversion operator must run before the next property is read");
+            results.RecordedValues.Should().Equal(expectedUnits, because: "each observed value must be read from the converted result");
+            results.HasCompleted.Should().BeFalse(because: "further amount changes remain observable");
+        }
+
+        /// <summary>Verifies that a user-defined conversion keeps its own evaluation path alongside a built-in conversion.</summary>
+        [Fact]
+        public void UserDefinedAndBuiltInConversionsOnSameProperty_Changes_UseEachConversion()
+        {
+            // Arrange
+            var initialAmount = _randomizer.Int(1, ushort.MaxValue) + 0.5d;
+            var changedAmount = initialAmount + _randomizer.Int(1, ushort.MaxValue);
+            var model = new ObservablePrice { Amount = initialAmount };
+            var expectedUnits = new[] { ((Money)initialAmount).WholeUnits, ((Money)changedAmount).WholeUnits };
+            var expectedScales = new[] { ((decimal)initialAmount).Scale, ((decimal)changedAmount).Scale };
+            using var moneySubscription = model.WhenValueChanged(static price => ((Money)price.Amount).WholeUnits)
+                .RecordValues(out var units);
+            using var decimalSubscription = model.WhenValueChanged(static price => ((decimal)price.Amount).Scale)
+                .RecordValues(out var scales);
+
+            // Act
+            model.Amount = changedAmount;
+
+            // Assert
+            units.Error.Should().BeNull(because: "the user-defined conversion must have a compatible factory");
+            scales.Error.Should().BeNull(because: "the built-in conversion must have a compatible factory");
+            units.RecordedValues.Should().Equal(expectedUnits, because: "the user-defined path reports whole units");
+            scales.RecordedValues.Should().Equal(expectedScales, because: "the built-in path reports the decimal scale");
+            units.HasCompleted.Should().BeFalse(because: "the user-defined observation remains active");
+            scales.HasCompleted.Should().BeFalse(because: "the built-in observation remains active");
+        }
+
+        /// <summary>Verifies that equivalent converted paths share a factory regardless of lambda parameter names.</summary>
+        [Fact]
+        public void EquivalentConversionPaths_DifferentParameterNames_ReuseFactory()
+        {
+            // Arrange
+            Expression<Func<ObservablePrice, byte>> first = static price => ((decimal)price.Amount).Scale;
+            Expression<Func<ObservablePrice, byte>> second = static otherPrice => ((decimal)otherPrice.Amount).Scale;
+            var firstFactory = ObservablePropertyFactoryCache.Instance.GetFactory(first);
+
+            // Act
+            var secondFactory = ObservablePropertyFactoryCache.Instance.GetFactory(second);
+
+            // Assert
+            secondFactory.Should().BeSameAs(firstFactory, because: "parameter names do not change a property's evaluation path");
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.DeepChain.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.DeepChain.cs
new file mode 100644
index 000000000..c3d950cb9
--- /dev/null
+++ b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.DeepChain.cs
@@ -0,0 +1,197 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reactive.Concurrency;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Binding;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Binding;
+
+public static partial class WhenPropertyChangedFixture
+{
+    public partial class UnitTests
+    {
+        [Theory]
+        [InlineData(true, false)]
+        [InlineData(true, true)]
+        [InlineData(false, true)]
+        public void DeepChain_InitialGetterThrows_DefaultErrorHandler_DetachesEveryHandler(bool notifyOnInitialValue, bool failBeforeLeaf)
+        {
+            // Arrange
+            var error = new InvalidOperationException();
+            var leaf = new ObservablePrice { Amount = ObservedAmount, ReadError = failBeforeLeaf ? null : error };
+            var child = new ObservablePrice { Child = leaf, ChildReadError = failBeforeLeaf ? error : null };
+            var root = new ObservablePrice { Child = child };
+            var models = new[] { root, child, leaf };
+            var source = root.WhenValueChanged(static price => price.Child!.Child!.Amount, notifyOnInitialValue);
+
+            // Act
+            Action subscribe = () =>
+            {
+                using var subscription = source.Subscribe();
+            };
+
+            // Assert
+            subscribe.Should().Throw<Exception>(because: "the default Rx error handler must rethrow initialization failures")
+                .Which.GetBaseException().Should().BeSameAs(error, because: "the failure must originate in the observed getter");
+            root.WasSubscribed.Should().BeTrue(because: "the root handler must attach before its child is read");
+            child.WasSubscribed.Should().BeTrue(because: "the intermediate handler must attach before its child is read");
+            leaf.WasSubscribed.Should().Be(!failBeforeLeaf, because: "the leaf is reachable only if the intermediate getter succeeds");
+            models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
+                because: "failed initialization must release handlers at every visited level");
+        }
+
+        [Theory]
+        [InlineData(true, false)]
+        [InlineData(true, true)]
+        [InlineData(false, true)]
+        public void DeepChain_InitialGetterThrows_ErrorIsRecordedAndEveryHandlerDetached(bool notifyOnInitialValue, bool failBeforeLeaf)
+        {
+            // Arrange
+            var error = new InvalidOperationException();
+            var leaf = new ObservablePrice { Amount = ObservedAmount, ReadError = failBeforeLeaf ? null : error };
+            var child = new ObservablePrice { Child = leaf, ChildReadError = failBeforeLeaf ? error : null };
+            var root = new ObservablePrice { Child = child };
+            var models = new[] { root, child, leaf };
+
+            // Act
+            using var subscription = root.WhenPropertyChanged(static price => price.Child!.Child!.Amount, notifyOnInitialValue)
+                .RecordValues(out var results);
+
+            // Assert
+            results.Error.Should().NotBeNull(because: "chain getter failures must be delivered through OnError");
+            results.Error!.GetBaseException().Should().BeSameAs(error, because: "the failure must originate in the observed getter");
+            results.RecordedValues.Should().BeEmpty(because: "the chain did not produce an obtainable value");
+            results.HasCompleted.Should().BeFalse(because: "OnError is the terminal notification");
+            root.WasSubscribed.Should().BeTrue(because: "the root handler must attach before its child is read");
+            child.WasSubscribed.Should().BeTrue(because: "the intermediate handler must attach before its child is read");
+            leaf.WasSubscribed.Should().Be(!failBeforeLeaf, because: "the leaf is reachable only if the intermediate getter succeeds");
+            models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
+                because: "OnError must release every handler before Subscribe returns");
+        }
+
+        [Fact]
+        public void DeepChain_InitialObserverThrows_DetachesEveryHandler()
+        {
+            // Arrange
+            var leaf = new ObservablePrice { Amount = ObservedAmount };
+            var child = new ObservablePrice { Child = leaf };
+            var root = new ObservablePrice { Child = child };
+            var models = new[] { root, child, leaf };
+            var error = new InvalidOperationException();
+            var results = new ValueRecordingObserver<double>(ImmediateScheduler.Instance);
+            IObserver<double> observer = results;
+            var source = root.WhenValueChanged(static price => price.Child!.Child!.Amount);
+
+            // Act
+            Action subscribe = () =>
+            {
+                using var subscription = source.Subscribe(value =>
+                {
+                    observer.OnNext(value);
+                    throw error;
+                }, observer.OnError);
+            };
+
+            // Assert
+            subscribe.Should().Throw<InvalidOperationException>(because: "observer failures must escape Subscribe")
+                .Which.Should().BeSameAs(error, because: "the original observer failure must be preserved");
+            results.RecordedValues.Should().Equal(new[] { ObservedAmount }, because: "the failure occurs during initial delivery");
+            results.Error.Should().BeNull(because: "an observer failure must not be converted into an OnError notification");
+            models.Should().OnlyContain(model => model.WasSubscribed, because: "each observable level must be registered before it is read");
+            models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
+                because: "failed initialization must release every handler, not just the root handler");
+        }
+
+        [Fact]
+        public void DeepChain_MidChainSwap_DeeperLevelsRetargetCorrectly()
+        {
+            // Mid-chain swap on a 4-level chain. When level 3 is reassigned, the leaf subscription
+            // must re-attach against the new subtree; events on the old subtree must be ignored
+            // (its notifier subscription was disposed).
+            var l1 = new Level1
+            {
+                Child = new Level2
+                {
+                    Child = new Level3
+                    {
+                        Child = new Level4 { Leaf = 10 },
+                    },
+                },
+            };
+
+            var emissions = new List<int>();
+            using var sub = l1.WhenPropertyChanged(x => x.Child!.Child!.Child!.Leaf, notifyOnInitialValue: true)
+                .Subscribe(pv => emissions.Add(pv.Value));
+
+            emissions.Should().Equal(new[] { 10 }, "initial emission");
+
+            var originalLeaf = l1.Child!.Child!.Child!;
+
+            var newL4 = new Level4 { Leaf = 20 };
+            l1.Child!.Child!.Child = newL4;
+
+            emissions.Should().Equal(new[] { 10, 20 }, "mid-chain swap emits the new leaf value");
+
+            newL4.Leaf = 30;
+            emissions.Should().Equal(new[] { 10, 20, 30 }, "leaf event on new subtree is captured");
+
+            originalLeaf.Leaf = 999;
+            emissions.Should().Equal(new[] { 10, 20, 30 }, "leaf event on detached subtree is ignored");
+        }
+
+        [Fact]
+        public void DeepChain_NotifyInitialFalse_DoesNotDedupSameValuedEvents()
+        {
+            var parent = new ParentModel { Child = new ChildModel { Age = 1 } };
+            var emissions = new List<int>();
+
+            using var sub = parent.WhenPropertyChanged(p => p.Child!.Age, notifyOnInitialValue: false)
+                .Subscribe(pv => emissions.Add(pv.Value));
+
+            parent.Child!.Age = 7;
+            parent.Child!.Age = 7;
+
+            emissions.Should().Equal(new[] { 7, 7 });
+        }
+
+        [Fact]
+        public void DeepChain_PostSwap_LeafEventOnNewChild_Captured()
+        {
+            // After parent.Child is reassigned, the leaf-level subscription must be re-attached
+            // against the new child. A subsequent leaf mutation on the new child must be captured.
+            var parent = new ParentModel { Child = new ChildModel { Age = 10 } };
+            var emissions = new List<int>();
+
+            using var sub = parent.WhenPropertyChanged(p => p.Child!.Age, notifyOnInitialValue: true)
+                .Subscribe(pv => emissions.Add(pv.Value));
+
+            var newChild = new ChildModel { Age = 20 };
+            parent.Child = newChild;
+            newChild.Age = 30;
+
+            emissions.Should().Equal(new[] { 10, 20, 30 });
+        }
+
+        [Fact]
+        public void DeepChain_NotifyInitialTrue_DoesNotDedupSameValuedEvents()
+        {
+            var parent = new ParentModel { Child = new ChildModel { Age = 1 } };
+            var emissions = new List<int>();
+
+            using var sub = parent.WhenPropertyChanged(p => p.Child!.Age, notifyOnInitialValue: true)
+                .Subscribe(pv => emissions.Add(pv.Value));
+
+            parent.Child!.Age = 1;
+            parent.Child!.Age = 1;
+            parent.Child!.Age = 1;
+
+            emissions.Should().Equal(new[] { 1, 1, 1, 1 });
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.Shallow.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.Shallow.cs
new file mode 100644
index 000000000..bb60b30f7
--- /dev/null
+++ b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.Shallow.cs
@@ -0,0 +1,135 @@
+using System;
+using System.Collections.Generic;
+using System.Reactive.Concurrency;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Binding;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Binding;
+
+public static partial class WhenPropertyChangedFixture
+{
+    public partial class UnitTests
+    {
+        [Fact]
+        public void Shallow_InitialGetterThrows_DefaultErrorHandler_DetachesHandler()
+        {
+            // Arrange
+            var error = new InvalidOperationException();
+            var model = new ObservablePrice { Amount = ObservedAmount, ReadError = error };
+            var source = model.WhenValueChanged(static price => price.Amount);
+
+            // Act
+            Action subscribe = () =>
+            {
+                using var subscription = source.Subscribe();
+            };
+
+            // Assert
+            subscribe.Should().Throw<InvalidOperationException>(because: "the default Rx error handler must rethrow the getter failure")
+                .Which.Should().BeSameAs(error, because: "the original getter failure must be preserved");
+            model.WasSubscribed.Should().BeTrue(because: "registration must precede the initial value read");
+            model.HandlerCount.Should().Be(0, because: "failed initialization must not retain the event handler");
+        }
+
+        [Fact]
+        public void Shallow_InitialGetterThrows_ErrorIsRecordedAndHandlerDetached()
+        {
+            // Arrange
+            var error = new InvalidOperationException();
+            var model = new ObservablePrice { Amount = ObservedAmount, ReadError = error };
+
+            // Act
+            using var subscription = model.WhenPropertyChanged(static price => price.Amount)
+                .RecordValues(out var results);
+
+            // Assert
+            results.Error.Should().BeSameAs(error, because: "getter failures must be delivered through OnError");
+            results.RecordedValues.Should().BeEmpty(because: "the initial getter did not produce a value");
+            results.HasCompleted.Should().BeFalse(because: "OnError is the terminal notification");
+            model.WasSubscribed.Should().BeTrue(because: "registration must precede the initial value read");
+            model.HandlerCount.Should().Be(0, because: "OnError must release the handler before Subscribe returns");
+        }
+
+        [Fact]
+        public void Shallow_InitialObserverThrows_DetachesHandler()
+        {
+            // Arrange
+            var model = new ObservablePrice { Amount = ObservedAmount };
+            var error = new InvalidOperationException();
+            var results = new ValueRecordingObserver<double>(ImmediateScheduler.Instance);
+            IObserver<double> observer = results;
+            var source = model.WhenValueChanged(static price => price.Amount);
+
+            // Act
+            Action subscribe = () =>
+            {
+                using var subscription = source.Subscribe(value =>
+                {
+                    observer.OnNext(value);
+                    throw error;
+                }, observer.OnError);
+            };
+
+            // Assert
+            subscribe.Should().Throw<InvalidOperationException>(because: "observer failures must escape Subscribe")
+                .Which.Should().BeSameAs(error, because: "the original observer failure must be preserved");
+            results.RecordedValues.Should().Equal(new[] { ObservedAmount }, because: "the failure occurs during initial delivery");
+            results.Error.Should().BeNull(because: "an observer failure must not be converted into an OnError notification");
+            model.WasSubscribed.Should().BeTrue(because: "registration must precede the initial value read");
+            model.HandlerCount.Should().Be(0, because: "a throwing Subscribe cannot return a disposable to its caller");
+        }
+
+        [Fact]
+        public void Shallow_NotifyInitialFalse_DoesNotDedupSameValuedEvents()
+        {
+            var model = new TestModel { Value = 10 };
+            var emissions = new List<int>();
+
+            using var sub = model.WhenPropertyChanged(m => m.Value, notifyOnInitialValue: false)
+                .Subscribe(pv => emissions.Add(pv.Value));
+
+            model.Value = 42;
+            model.Value = 42;
+
+            emissions.Should().Equal(new[] { 42, 42 });
+        }
+
+        [Fact]
+        public void Shallow_NotifyInitialFalse_SubscribesHandlerBeforeReturning()
+        {
+            // notifyOnInitialValue=false: Subscribe must return only after the PropertyChanged handler
+            // is attached. A setter that fires immediately after Subscribe returns must reach the
+            // observer.
+            var model = new TestModel { Value = 10 };
+            var emissions = new List<int>();
+
+            using var sub = model.WhenPropertyChanged(m => m.Value, notifyOnInitialValue: false)
+                .Subscribe(pv => emissions.Add(pv.Value));
+
+            model.Value = 20;
+
+            emissions.Should().Equal(new[] { 20 });
+        }
+
+        [Fact]
+        public void Shallow_NotifyInitialTrue_DoesNotDedupSameValuedEvents()
+        {
+            var model = new TestModel { Value = 10 };
+            var emissions = new List<int>();
+
+            using var sub = model.WhenPropertyChanged(m => m.Value, notifyOnInitialValue: true)
+                .Subscribe(pv => emissions.Add(pv.Value));
+
+            model.Value = 10;
+            model.Value = 10;
+            model.Value = 10;
+
+            emissions.Should().Equal(new[] { 10, 10, 10, 10 });
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.Subscription.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.Subscription.cs
new file mode 100644
index 000000000..5cf37f3b9
--- /dev/null
+++ b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.Subscription.cs
@@ -0,0 +1,72 @@
+using System.Linq;
+using System.Reactive.Linq;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Binding;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Binding;
+
+public static partial class WhenPropertyChangedFixture
+{
+    public partial class UnitTests
+    {
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public void Subscription_ExplicitDisposal_ReleasesHandlers(bool deepChain)
+        {
+            // Arrange
+            var leaf = new ObservablePrice { Amount = ObservedAmount };
+            var child = new ObservablePrice { Child = leaf };
+            var root = new ObservablePrice { Child = child };
+            var models = deepChain ? new[] { root, child, leaf } : new[] { leaf };
+            var source = deepChain
+                ? root.WhenValueChanged(static price => price.Child!.Child!.Amount)
+                : leaf.WhenValueChanged(static price => price.Amount);
+            using var subscription = source.RecordValues(out var results);
+            var attachedHandlerCounts = models.Select(model => model.HandlerCount).ToArray();
+
+            // Act
+            subscription.Dispose();
+
+            // Assert
+            attachedHandlerCounts.Should().OnlyContain(count => count == 1, because: "each visited object must stay subscribed after initialization");
+            models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
+                because: "disposing the returned subscription must release every retained handler");
+            results.RecordedValues.Should().Equal(new[] { ObservedAmount }, because: "initialization must publish the observed value");
+            results.Error.Should().BeNull(because: "explicit disposal is not an observation failure");
+            results.HasCompleted.Should().BeFalse(because: "unsubscribing does not publish a completion notification");
+        }
+
+        [Theory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public void Subscription_SynchronousCompletion_ReleasesHandlers(bool deepChain)
+        {
+            // Arrange
+            var leaf = new ObservablePrice { Amount = ObservedAmount };
+            var child = new ObservablePrice { Child = leaf };
+            var root = new ObservablePrice { Child = child };
+            var models = deepChain ? new[] { root, child, leaf } : new[] { leaf };
+            var source = deepChain
+                ? root.WhenValueChanged(static price => price.Child!.Child!.Amount)
+                : leaf.WhenValueChanged(static price => price.Amount);
+
+            // Act
+            using var subscription = source.Take(1)
+                .RecordValues(out var results);
+
+            // Assert
+            results.RecordedValues.Should().Equal(new[] { ObservedAmount }, because: "the requested initial value must be delivered");
+            results.Error.Should().BeNull(because: "taking an initial value is normal completion");
+            results.HasCompleted.Should().BeTrue(because: "Take completes after receiving its requested value");
+            models.Should().OnlyContain(model => model.WasSubscribed, because: "handlers must attach before initial delivery");
+            models.Select(model => model.HandlerCount).Should().OnlyContain(count => count == 0,
+                because: "synchronous completion must release handlers before Subscribe returns");
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.cs
new file mode 100644
index 000000000..a25da1c05
--- /dev/null
+++ b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.UnitTests.cs
@@ -0,0 +1,49 @@
+using System;
+using System.Linq;
+
+using Bogus;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Binding;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Binding;
+ 
+public static partial class WhenPropertyChangedFixture
+{
+    public partial class UnitTests
+    {
+        private readonly Randomizer _randomizer
+            = new(0x35C1_709B);
+
+        // https://github.com/reactivemarbles/DynamicData/issues/1149
+        [Fact]
+        public void ExpressionContainsImplicitInterfaceCast()
+        {
+            var child = new ChildModel()
+            {
+                Age = 10
+            };
+            
+            using var subscription = ObserveAge(child)
+                .RecordValues(out var results);
+
+            results.Error.Should().BeNull("no errors should have occurred");
+            results.RecordedValues.Should().ContainSingle("the initial value of the observed expression should have been published");
+            results.RecordedValues[0].Should().Be(child.Age, "the initial value of the observed expression should have been published");
+
+            ++child.Age;
+
+            results.Error.Should().BeNull("no errors should have occurred");
+            results.RecordedValues.Skip(1).Should().ContainSingle("the value of the observed expression changed once");
+            results.RecordedValues[1].Should().Be(child.Age, "the correct value should have been published");
+
+            static IObservable<int> ObserveAge<T>(T source)
+                where T : IHasAge
+                => source.WhenValueChanged(source => source.Age);
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.cs
new file mode 100644
index 000000000..2bfded56b
--- /dev/null
+++ b/src/DynamicData.Tests/Binding/WhenPropertyChangedFixture.cs
@@ -0,0 +1,345 @@
+using System;
+using System.ComponentModel;
+
+namespace DynamicData.Tests.Binding;
+
+public static partial class WhenPropertyChangedFixture
+{
+    private const double ObservedAmount = 41.375;
+
+    private static decimal ConvertAmount(double amount)
+        => (decimal)amount;
+
+    private static Deep1 NewDeepChain(int leaf)
+        => new Deep1 { Child = NewDeep2(leaf) };
+
+    private static Deep2 NewDeep2(int leaf)
+        => new Deep2 { Child = NewDeep3(leaf) };
+
+    private static Deep3 NewDeep3(int leaf)
+        => new Deep3 { Child = NewDeep4(leaf) };
+
+    private static Deep4 NewDeep4(int leaf) =>
+        new Deep4 { Child = new Deep5 { Leaf = leaf } };
+
+    private static decimal TruncateAmount(double amount)
+        => decimal.Truncate((decimal)amount);
+
+    private sealed class Item : INotifyPropertyChanged
+    {
+        private int _value;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public int Id { get; init; }
+
+        public int Value
+        {
+            get => _value;
+            set
+            {
+                _value = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Value)));
+            }
+        }
+    }
+
+    private sealed class KeyedActivable : INotifyPropertyChanged
+    {
+        private bool _activated;
+
+        public KeyedActivable(int id)
+        {
+            Id = id;
+        }
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public int Id { get; }
+
+        public bool Activated
+        {
+            get => _activated;
+            set
+            {
+                if (_activated == value) return;
+                _activated = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Activated)));
+            }
+        }
+    }
+
+    private sealed class Money
+    {
+        private Money(double amount) => WholeUnits = (int)amount;
+
+        public int WholeUnits { get; }
+
+        public static explicit operator Money(double amount) => new(amount);
+    }
+
+    public sealed class ObservablePrice
+        : INotifyPropertyChanged
+    {
+        private double _amount;
+        private ObservablePrice? _child;
+        private double _otherAmount;
+        private PropertyChangedEventHandler? _propertyChanged;
+
+        public event PropertyChangedEventHandler? PropertyChanged
+        {
+            add
+            {
+                WasSubscribed = true;
+                _propertyChanged += value;
+            }
+
+            remove => _propertyChanged -= value;
+        }
+
+        public double Amount
+        {
+            get => ReadError is null ? _amount : throw ReadError;
+            set
+            {
+                _amount = value;
+                _propertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Amount)));
+            }
+        }
+
+        public ObservablePrice? Child
+        {
+            get => ChildReadError is null ? _child : throw ChildReadError;
+            init => _child = value;
+        }
+
+        public InvalidOperationException? ChildReadError { get; init; }
+
+        public int HandlerCount => _propertyChanged?.GetInvocationList().Length ?? 0;
+
+        public InvalidOperationException? ReadError { get; init; }
+
+        public double OtherAmount
+        {
+            get => _otherAmount;
+            set
+            {
+                _otherAmount = value;
+                _propertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(OtherAmount)));
+            }
+        }
+
+        public bool WasSubscribed { get; private set; }
+    }
+    
+    private interface IHasAge
+        : INotifyPropertyChanged
+    {
+        int Age { get; }
+    }
+
+    private sealed class TestModel : INotifyPropertyChanged
+    {
+        private int _value;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public int Value
+        {
+            get => _value;
+            set
+            {
+                _value = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Value)));
+            }
+        }
+    }
+
+    private sealed class ParentModel : INotifyPropertyChanged
+    {
+        private ChildModel? _child;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public ChildModel? Child
+        {
+            get => _child;
+            set
+            {
+                _child = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
+            }
+        }
+    }
+
+    private sealed class ChildModel
+        : IHasAge
+    {
+        private int _age;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public int Age
+        {
+            get => _age;
+            set
+            {
+                _age = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Age)));
+            }
+        }
+    }
+
+    private sealed class Deep1 : INotifyPropertyChanged
+    {
+        private Deep2? _child;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public Deep2? Child
+        {
+            get => _child;
+            set
+            {
+                _child = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
+            }
+        }
+    }
+
+    private sealed class Deep2 : INotifyPropertyChanged
+    {
+        private Deep3? _child;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public Deep3? Child
+        {
+            get => _child;
+            set
+            {
+                _child = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
+            }
+        }
+    }
+
+    private sealed class Deep3 : INotifyPropertyChanged
+    {
+        private Deep4? _child;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public Deep4? Child
+        {
+            get => _child;
+            set
+            {
+                _child = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
+            }
+        }
+    }
+
+    private sealed class Deep4 : INotifyPropertyChanged
+    {
+        private Deep5? _child;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public Deep5? Child
+        {
+            get => _child;
+            set
+            {
+                _child = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
+            }
+        }
+    }
+
+    private sealed class Deep5 : INotifyPropertyChanged
+    {
+        private int _leaf;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public int Leaf
+        {
+            get => _leaf;
+            set
+            {
+                _leaf = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Leaf)));
+            }
+        }
+    }
+
+    private sealed class Level1 : INotifyPropertyChanged
+    {
+        private Level2? _child;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public Level2? Child
+        {
+            get => _child;
+            set
+            {
+                _child = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
+            }
+        }
+    }
+
+    private sealed class Level2 : INotifyPropertyChanged
+    {
+        private Level3? _child;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public Level3? Child
+        {
+            get => _child;
+            set
+            {
+                _child = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
+            }
+        }
+    }
+
+    private sealed class Level3 : INotifyPropertyChanged
+    {
+        private Level4? _child;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public Level4? Child
+        {
+            get => _child;
+            set
+            {
+                _child = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
+            }
+        }
+    }
+
+    private sealed class Level4 : INotifyPropertyChanged
+    {
+        private int _leaf;
+
+        public event PropertyChangedEventHandler? PropertyChanged;
+
+        public int Leaf
+        {
+            get => _leaf;
+            set
+            {
+                _leaf = value;
+                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Leaf)));
+            }
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Binding/WhenPropertyChangedRaceFixture.cs b/src/DynamicData.Tests/Binding/WhenPropertyChangedRaceFixture.cs
deleted file mode 100644
index 5c8d073c8..000000000
--- a/src/DynamicData.Tests/Binding/WhenPropertyChangedRaceFixture.cs
+++ /dev/null
@@ -1,554 +0,0 @@
-// Copyright (c) 2011-2025 Roland Pheasant. All rights reserved.
-// Roland Pheasant licenses this file to you under the MIT license.
-// See the LICENSE file in the project root for full license information.
-
-using System;
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Linq;
-using System.Reactive;
-using System.Reactive.Concurrency;
-using System.Reactive.Linq;
-using System.Threading;
-using System.Threading.Tasks;
-
-using DynamicData.Binding;
-using DynamicData.Tests.Utilities;
-
-using FluentAssertions;
-
-using Xunit;
-
-namespace DynamicData.Tests.Binding;
-
-/// <summary>
-/// Multi-threaded race tests for <see cref="NotifyPropertyChangedEx.WhenPropertyChanged{TObject, TProperty}"/>.
-/// Each test forces concurrency between the operator's subscribe call (or chain re-walk) and one or more
-/// <see cref="System.ComponentModel.INotifyPropertyChanged.PropertyChanged"/> notifiers firing on other threads.
-/// </summary>
-public sealed class WhenPropertyChangedRaceFixture
-{
-    private static readonly TimeSpan ConditionTimeout = TimeSpan.FromSeconds(30);
-
-    [Fact]
-    public async Task Shallow_ConcurrentMutationDuringInitialEmit_NotDropped()
-    {
-        var item = new Item()
-        {
-            Id = 1,
-            Value = 10
-        };
-
-        var whenSubscribing = new ManualResetEventSlim();
-        var whenValueChanged = new ManualResetEventSlim();
-
-        var source = item.WhenPropertyChanged(
-            propertyAccessor:       static item => item.Value,
-            notifyOnInitialValue:   true);
-
-        var observedValues = new List<int>();
-        var observer = Observer.Create<PropertyValue<Item, int>>(propertyValue =>
-        {
-            observedValues.Add(propertyValue.Value);
-
-            whenSubscribing.Set();
-            whenValueChanged.Wait();
-        });
-
-        await Task.WhenAll(
-            Task.Run(() =>
-            {
-                using var subscription = source.Subscribe(observer);
-            }),
-            Task.Run(() =>
-            {
-                whenSubscribing.Wait();
-
-                item.Value = 20;
-
-                whenValueChanged.Set();
-            }));
-
-        observedValues.Should().BeEquivalentTo(
-            expectation:    new [] { 10, 20 },
-            config:         options => options.WithStrictOrdering(),
-            because:        "All change events occurring after publication of the initial value should be captured and forwarded.");
-    }
-
-    [Fact]
-    public async Task DeepChain_ConcurrentLeafMutationDuringInitialEmit_NotDropped()
-    {
-        // Deep-chain version of the above. The observer blocks inside its OnNext for the initial
-        // leaf value while a second thread mutates the leaf.
-        var parent = new ParentModel { Child = new ChildModel { Age = 10 } };
-
-        var whenSubscribing = new ManualResetEventSlim();
-        var whenValueChanged = new ManualResetEventSlim();
-
-        var emissions = new List<int>();
-        var observer = Observer.Create<PropertyValue<ParentModel, int>>(pv =>
-        {
-            emissions.Add(pv.Value);
-            whenSubscribing.Set();
-            whenValueChanged.Wait();
-        });
-
-        var source = parent.WhenPropertyChanged(static p => p.Child!.Age, notifyOnInitialValue: true);
-
-        await Task.WhenAll(
-            Task.Run(() =>
-            {
-                using var subscription = source.Subscribe(observer);
-            }),
-            Task.Run(() =>
-            {
-                whenSubscribing.Wait();
-                parent.Child!.Age = 20;
-                whenValueChanged.Set();
-            })).WaitAsync(ConditionTimeout);
-
-        emissions.Should().Equal(new[] { 10, 20 });
-    }
-
-    [Fact]
-    public async Task DeepChain_ConcurrentParentSwap_LeafEventOnWinnerNotDropped()
-    {
-        // Two threads concurrently swap parent.Child. After both swaps complete, a leaf mutation
-        // on the current child must be captured. SharedDeliveryQueue serialises the level-0
-        // signals on the drainer, so the final level-1 subscription always targets parent.Child's
-        // current value.
-        const int iterations = 50;
-        var losses = 0;
-
-        for (var iter = 0; iter < iterations; iter++)
-        {
-            var parent = new ParentModel { Child = new ChildModel { Age = 0 } };
-            var emissions = new List<int>();
-
-            using var sub = parent.WhenPropertyChanged(p => p.Child!.Age, notifyOnInitialValue: false)
-                .Subscribe(pv => { lock (emissions) emissions.Add(pv.Value); });
-
-            var newChild1 = new ChildModel { Age = 1 };
-            var newChild2 = new ChildModel { Age = 2 };
-
-            using var barrier = new Barrier(2);
-            var taskA = Task.Run(() => { barrier.SignalAndWait(); parent.Child = newChild1; });
-            var taskB = Task.Run(() => { barrier.SignalAndWait(); parent.Child = newChild2; });
-            await Task.WhenAll(taskA, taskB).WaitAsync(ConditionTimeout);
-
-            var winner = parent.Child;
-            if (winner is null)
-            {
-                continue;
-            }
-
-            winner.Age = 99;
-
-            WaitForCondition(() => { lock (emissions) return emissions.Contains(99); });
-
-            lock (emissions)
-            {
-                if (!emissions.Contains(99))
-                {
-                    losses++;
-                }
-            }
-        }
-
-        losses.Should().Be(0, $"out of {iterations} iterations, {losses} dropped the leaf event on the post-swap winner");
-    }
-
-    [Fact]
-    public async Task DeepChain_FiveLevels_AllLevelsMutatedConcurrently_FinalEmissionMatchesActual()
-    {
-        // Torture: five worker threads each mutating at a different level of a 5-level chain.
-        // Mutations that land on detached subtrees are ignored (their notifier subscriptions were
-        // disposed by ResubscribeFrom). Mutations on the live chain reach the drainer.
-        //
-        // Three invariants per iteration:
-        //   (a) Rx contract: ValidateSynchronization catches any concurrent OnNext on the user
-        //       observer (a SharedDeliveryQueue serialisation failure).
-        //   (b) Value legality: every emission must be a value that some thread legitimately
-        //       wrote.
-        //   (c) Final consistency: after Task.WhenAll the drainer continues until the queue is
-        //       empty. The last processed signal triggers a ReadCurrent against the now-frozen
-        //       chain state, so emissions.Last() == ReadCurrent().
-        const int iterations = 50;
-        const int mutationsPerThread = 200;
-        var mismatches = 0;
-
-        for (var iter = 0; iter < iterations; iter++)
-        {
-            var root = NewDeepChain(0);
-            var emissions = new List<int>();
-
-            using var sub = root.WhenPropertyChanged(r => r.Child!.Child!.Child!.Child!.Leaf, notifyOnInitialValue: true)
-                .ValidateSynchronization()
-                .Subscribe(pv => { lock (emissions) emissions.Add(pv.Value); });
-
-            using var barrier = new Barrier(5);
-            var iterSeed = iter * 10_000;
-            var tasks = new[]
-            {
-                Task.Run(() =>
-                {
-                    barrier.SignalAndWait();
-                    for (var i = 0; i < mutationsPerThread; i++)
-                    {
-                        root.Child = NewDeep2(iterSeed + 40_000 + i);
-                    }
-                }),
-                Task.Run(() =>
-                {
-                    barrier.SignalAndWait();
-                    for (var i = 0; i < mutationsPerThread; i++)
-                    {
-                        var l2 = root.Child;
-                        if (l2 is not null) l2.Child = NewDeep3(iterSeed + 30_000 + i);
-                    }
-                }),
-                Task.Run(() =>
-                {
-                    barrier.SignalAndWait();
-                    for (var i = 0; i < mutationsPerThread; i++)
-                    {
-                        var l3 = root.Child?.Child;
-                        if (l3 is not null) l3.Child = NewDeep4(iterSeed + 20_000 + i);
-                    }
-                }),
-                Task.Run(() =>
-                {
-                    barrier.SignalAndWait();
-                    for (var i = 0; i < mutationsPerThread; i++)
-                    {
-                        var l4 = root.Child?.Child?.Child;
-                        if (l4 is not null) l4.Child = new Deep5 { Leaf = iterSeed + 10_000 + i };
-                    }
-                }),
-                Task.Run(() =>
-                {
-                    barrier.SignalAndWait();
-                    for (var i = 0; i < mutationsPerThread; i++)
-                    {
-                        var l5 = root.Child?.Child?.Child?.Child;
-                        if (l5 is not null) l5.Leaf = i;
-                    }
-                }),
-            };
-
-            await Task.WhenAll(tasks).WaitAsync(ConditionTimeout);
-
-            var actualFinal = root.Child!.Child!.Child!.Child!.Leaf;
-
-            WaitForCondition(() => { lock (emissions) return emissions.Count > 0 && emissions[^1] == actualFinal; });
-
-            var legal = new HashSet<int> { 0 };
-            for (var i = 0; i < mutationsPerThread; i++)
-            {
-                legal.Add(i);
-                legal.Add(iterSeed + 10_000 + i);
-                legal.Add(iterSeed + 20_000 + i);
-                legal.Add(iterSeed + 30_000 + i);
-                legal.Add(iterSeed + 40_000 + i);
-            }
-
-            lock (emissions)
-            {
-                emissions.Should().NotBeEmpty($"iter {iter}: notifyOnInitialValue=true requires at least the initial emission");
-                emissions[0].Should().Be(0, $"iter {iter}: first emission must be the initial value");
-
-                var illegal = emissions.Where(v => !legal.Contains(v)).ToList();
-                illegal.Should().BeEmpty($"iter {iter}: every emission must be a value some thread wrote; saw {string.Join(",", illegal.Take(5))}");
-
-                if (emissions.Count == 0 || emissions[^1] != actualFinal)
-                {
-                    mismatches++;
-                }
-            }
-        }
-
-        mismatches.Should().Be(0, $"out of {iterations} iterations, {mismatches} ended with the last emission not matching the actual final chain leaf");
-    }
-
-    [Fact(Skip = "AutoRefresh has a separate concurrency bug; tracked separately")]
-    public async Task AutoRefreshThenFilter_ConcurrentAddsAndPropertyActivation_AllItemsObserved()
-    {
-        // One adder thread sequentially adds items to the cache while a single flipper thread
-        // concurrently sets each item's Activated to true. Final filter contents must include
-        // every item (every item ends Activated=true).
-        //
-        // KeyedActivable's setter only raises PropertyChanged on actual value change, so a
-        // dropped false->true transition is unrecoverable.
-        //
-        // The race lives in AutoRefresh's internal Publish multicast: Sub 1 (Filter path)
-        // receives the Add and reads the property before Sub 2 (MergeMany) subscribes the
-        // per-item refresh handler. A concurrent flip landing in that gap is dropped. This
-        // is not a WhenPropertyChanged issue: AutoRefresh calls WhenPropertyChanged with
-        // notifyInitial=false, so the per-item subscribe attaches the handler immediately
-        // and has no internal race window.
-        const int iterations = 100;
-        const int itemCount = 200;
-
-        for (var iter = 0; iter < iterations; iter++)
-        {
-            using var cache = new SourceCache<KeyedActivable, int>(x => x.Id);
-            var items = Enumerable.Range(0, itemCount).Select(i => new KeyedActivable(i)).ToList();
-
-            using var results = cache.Connect()
-                .AutoRefresh(x => x.Activated)
-                .Filter(x => x.Activated)
-                .AsAggregator();
-
-            using var barrier = new Barrier(2);
-
-            var adder = Task.Run(() =>
-            {
-                barrier.SignalAndWait();
-                foreach (var item in items) cache.AddOrUpdate(item);
-            });
-
-            var flipper = Task.Run(() =>
-            {
-                barrier.SignalAndWait();
-                foreach (var item in items) item.Activated = true;
-            });
-
-            await Task.WhenAll(adder, flipper).WaitAsync(ConditionTimeout);
-
-            var expected = items.Select(x => x.Id).ToHashSet();
-            WaitForCondition(() => results.Data.Keys.ToHashSet().SetEquals(expected));
-
-            var actual = results.Data.Keys.ToHashSet();
-            actual.Should().BeEquivalentTo(expected, $"iter {iter}: every item ends Activated=true and must appear in the filter (missing: {string.Join(",", expected.Except(actual))})");
-            results.Error.Should().BeNull($"iter {iter}: pipeline must not error");
-        }
-    }
-
-    [Fact(Skip = "AutoRefresh has a separate concurrency bug; tracked separately")]
-    public async Task AutoRefreshThenFilter_DualSubscribers_AllItemsObserved()
-    {
-        // Two independent cache subscribers running on the ThreadPool:
-        //   Sub 1 (mutator): on every Add change, flips item.Activated to true
-        //   Sub 2 (filter chain): AutoRefresh + Filter (filter = Activated)
-        // Items start with Activated=false (filtered out). The mutator flips every item, so
-        // the final filter contents must include every item.
-        //
-        // Same root cause as the single-flipper variant above: AutoRefresh's internal Publish
-        // multicasts the Add to the Filter path before MergeMany subscribes the per-item
-        // refresh handler. The mutator's flip can land in that gap and be dropped.
-        const int iterations = 100;
-        const int itemCount = 200;
-
-        for (var iter = 0; iter < iterations; iter++)
-        {
-            using var cache = new SourceCache<KeyedActivable, int>(x => x.Id);
-            var items = Enumerable.Range(0, itemCount).Select(i => new KeyedActivable(i)).ToList();
-
-            using var mutator = cache.Connect()
-                .ObserveOn(TaskPoolScheduler.Default)
-                .Subscribe(changes =>
-                {
-                    foreach (var change in changes)
-                    {
-                        if (change.Reason == ChangeReason.Add)
-                        {
-                            change.Current.Activated = true;
-                        }
-                    }
-                });
-
-            using var results = cache.Connect()
-                .ObserveOn(TaskPoolScheduler.Default)
-                .AutoRefresh(x => x.Activated)
-                .Filter(x => x.Activated)
-                .AsAggregator();
-
-            foreach (var item in items) cache.AddOrUpdate(item);
-
-            var expected = items.Select(x => x.Id).ToHashSet();
-            WaitForCondition(() => results.Data.Keys.ToHashSet().SetEquals(expected));
-
-            var actual = results.Data.Keys.ToHashSet();
-            actual.Should().BeEquivalentTo(expected, $"iter {iter}: every item was flipped to Activated=true by the mutator and must appear in the filter (missing: {string.Join(",", expected.Except(actual))})");
-            results.Error.Should().BeNull($"iter {iter}: pipeline must not error");
-        }
-    }
-
-    private static Deep1 NewDeepChain(int leaf) =>
-        new Deep1 { Child = NewDeep2(leaf) };
-
-    private static Deep2 NewDeep2(int leaf) =>
-        new Deep2 { Child = NewDeep3(leaf) };
-
-    private static Deep3 NewDeep3(int leaf) =>
-        new Deep3 { Child = NewDeep4(leaf) };
-
-    private static Deep4 NewDeep4(int leaf) =>
-        new Deep4 { Child = new Deep5 { Leaf = leaf } };
-
-    private static void WaitForCondition(Func<bool> condition, TimeSpan? timeout = null) =>
-        SpinWait.SpinUntil(condition, timeout ?? ConditionTimeout);
-
-    private sealed class Item : INotifyPropertyChanged
-    {
-        private int _value;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public int Id { get; init; }
-
-        public int Value
-        {
-            get => _value;
-            set
-            {
-                _value = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Value)));
-            }
-        }
-    }
-
-    private sealed class ParentModel : INotifyPropertyChanged
-    {
-        private ChildModel? _child;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public ChildModel? Child
-        {
-            get => _child;
-            set
-            {
-                _child = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
-            }
-        }
-    }
-
-    private sealed class ChildModel : INotifyPropertyChanged
-    {
-        private int _age;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public int Age
-        {
-            get => _age;
-            set
-            {
-                _age = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Age)));
-            }
-        }
-    }
-
-    private sealed class Deep1 : INotifyPropertyChanged
-    {
-        private Deep2? _child;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public Deep2? Child
-        {
-            get => _child;
-            set
-            {
-                _child = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
-            }
-        }
-    }
-
-    private sealed class Deep2 : INotifyPropertyChanged
-    {
-        private Deep3? _child;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public Deep3? Child
-        {
-            get => _child;
-            set
-            {
-                _child = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
-            }
-        }
-    }
-
-    private sealed class Deep3 : INotifyPropertyChanged
-    {
-        private Deep4? _child;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public Deep4? Child
-        {
-            get => _child;
-            set
-            {
-                _child = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
-            }
-        }
-    }
-
-    private sealed class Deep4 : INotifyPropertyChanged
-    {
-        private Deep5? _child;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public Deep5? Child
-        {
-            get => _child;
-            set
-            {
-                _child = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Child)));
-            }
-        }
-    }
-
-    private sealed class Deep5 : INotifyPropertyChanged
-    {
-        private int _leaf;
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public int Leaf
-        {
-            get => _leaf;
-            set
-            {
-                _leaf = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Leaf)));
-            }
-        }
-    }
-
-    private sealed class KeyedActivable : INotifyPropertyChanged
-    {
-        private bool _activated;
-
-        public KeyedActivable(int id)
-        {
-            Id = id;
-        }
-
-        public event PropertyChangedEventHandler? PropertyChanged;
-
-        public int Id { get; }
-
-        public bool Activated
-        {
-            get => _activated;
-            set
-            {
-                if (_activated == value) return;
-                _activated = value;
-                PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Activated)));
-            }
-        }
-    }
-}
diff --git a/src/DynamicData.Tests/Cache/CrossCacheDeadlockStressTest.cs b/src/DynamicData.Tests/Cache/CrossCacheDeadlockStressTest.cs
index 8915bc6bc..a26b0a90f 100644
--- a/src/DynamicData.Tests/Cache/CrossCacheDeadlockStressTest.cs
+++ b/src/DynamicData.Tests/Cache/CrossCacheDeadlockStressTest.cs
@@ -31,6 +31,7 @@ namespace DynamicData.Tests.Cache;
 /// but not hardcoded). Proves: no deadlocks, correct final state, Rx compliance.
 /// </summary>
 public sealed class CrossCacheDeadlockStressTest
+    : IntegrationTestFixtureBase
 {
     // ════════════════════════════════════════════════════════════════
     // Bound constants — ONLY the seed and Min/Max bounds are hardcoded.
diff --git a/src/DynamicData.Tests/Cache/DeadlockTortureTest.cs b/src/DynamicData.Tests/Cache/DeadlockTortureTest.cs
index 4f4ddf9a4..deee5f15b 100644
--- a/src/DynamicData.Tests/Cache/DeadlockTortureTest.cs
+++ b/src/DynamicData.Tests/Cache/DeadlockTortureTest.cs
@@ -27,6 +27,7 @@ namespace DynamicData.Tests.Cache;
 /// On the PR branch (SynchronizeSafe queue-drain): no deadlock possible.
 /// </summary>
 public sealed class DeadlockTortureTest
+    : IntegrationTestFixtureBase
 {
     private const int ItemCount = 200;
     private const int Iterations = 50;
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheFixture.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheFixture.cs
deleted file mode 100644
index 949ec35bf..000000000
--- a/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheFixture.cs
+++ /dev/null
@@ -1,890 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Reactive;
-using System.Reactive.Concurrency;
-using System.Reactive.Disposables;
-using System.Reactive.Linq;
-using System.Reactive.Threading.Tasks;
-using System.Threading.Tasks;
-using Bogus;
-using DynamicData.Kernel;
-using DynamicData.Tests.Domain;
-using DynamicData.Tests.Utilities;
-using FluentAssertions;
-
-using Xunit;
-
-namespace DynamicData.Tests.Cache;
-
-public sealed class MergeManyChangeSetsCacheFixture : IDisposable
-{
-#if DEBUG
-    const int MarketCount = 5;
-    const int PricesPerMarket = 7;
-    const int RemoveCount = 3;
-#else
-    const int MarketCount = 101;
-    const int PricesPerMarket = 103;
-    const int RemoveCount = 53;
-#endif
-
-    const int ItemIdStride = 1000;
-    const decimal BasePrice = 10m;
-    const decimal PriceOffset = 10m;
-    const decimal HighestPrice = BasePrice + PriceOffset + 1.0m;
-    const decimal LowestPrice = BasePrice - 1.0m;
-
-    private readonly ISourceCache<IMarket, Guid> _marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
-
-    private readonly ChangeSetAggregator<IMarket, Guid> _marketCacheResults;
-
-    private readonly Faker<Market> _marketFaker;
-
-    private readonly Randomizer _randomizer;
-
-    public MergeManyChangeSetsCacheFixture()
-    {
-        _randomizer = new(0x21123737);
-        _marketFaker = Fakers.Market.WithSeed(_randomizer);
-        _marketCacheResults = _marketCache.Connect().AsAggregator();
-    }
-
-    [Theory]
-    [InlineData(5, 7)]
-    [InlineData(10, 50)]
-#if !DEBUG
-    [InlineData(10, 1_000)]
-    [InlineData(200, 500)]
-    [InlineData(1_000, 10)]
-#endif
-    public async Task MultiThreadedStressTest(int marketCount, int priceCount)
-    {
-        var MaxAddTime = TimeSpan.FromSeconds(0.250);
-        var MaxRemoveTime = TimeSpan.FromSeconds(0.100);
-
-        TimeSpan? GetRemoveTime() => _randomizer.Bool() ? _randomizer.TimeSpan(MaxRemoveTime) : null;
-
-        IObservable<Unit> AddRemoveStress(int marketCount, int priceCount, int parallel, IScheduler scheduler) =>
-            Observable.Create<Unit>(observer => new CompositeDisposable
-                (
-                    AddRemoveMarkets(marketCount, parallel, scheduler)
-                        .Subscribe(
-                            onNext: static _ => { },
-                            onError: observer.OnError),
-
-                    _marketCache.Connect()
-                        .MergeMany(market => AddRemovePrices((Market)market, priceCount, parallel, scheduler))
-                        .Subscribe(
-                            onNext: static _ => { },
-                            onError: observer.OnError,
-                            onCompleted: observer.OnCompleted)
-                ));
-
-        IObservable<IMarket> AddRemoveMarkets(int ownerCount, int parallel, IScheduler scheduler) =>
-            _marketFaker.IntervalGenerate(MaxAddTime, scheduler)
-                .Parallelize(ownerCount, parallel, obs => obs.StressAddRemove(_marketCache, _ => GetRemoveTime(), scheduler))
-                .Finally(_marketCache.Dispose);
-
-        IObservable<MarketPrice> AddRemovePrices(Market market, int priceCount, int parallel, IScheduler scheduler) =>
-            _randomizer.Interval(MaxAddTime, scheduler).Select(_ => market.CreateUniquePrice(_ => GetRandomPrice()))
-                .Parallelize(priceCount, parallel, obs => obs.StressAddRemove(market.PricesCache, _ => GetRemoveTime(), scheduler))
-                .Finally(market.PricesCache.Dispose);
-
-        var merged = _marketCache.Connect().MergeManyChangeSets(market => market.LatestPrices).Publish();
-        var adding = true;
-        var cacheCompleted = merged.LastOrDefaultAsync().ToTask();
-        using var priceResults = merged.AsAggregator();
-        using var connect = merged.Connect();
-
-        // Start asynchrononously modifying the parent list and the child lists
-        using var addingSub = AddRemoveStress(marketCount, priceCount, Environment.ProcessorCount, TaskPoolScheduler.Default)
-            .Finally(() => adding = false)
-            .Subscribe();
-
-        // Subscribe / unsubscribe over and over while the collections are being modified
-        do
-        {
-            // Ensure items are being added asynchronously before subscribing to changes
-            await Task.Yield();
-
-            {
-                // Subscribe
-                var mergedSub = merged.Subscribe();
-
-                // Let other threads run
-                await Task.Yield();
-
-                // Unsubscribe
-                mergedSub.Dispose();
-            }
-        }
-        while (adding);
-
-        // Wait for the source cache to finish delivering all notifications.
-        await cacheCompleted;
-
-        // Verify the results
-        CheckResultContents(_marketCacheResults, priceResults);
-    }
-
-    [Fact]
-    public void NullChecks()
-    {
-        // having
-        var emptyChangeSetObs = Observable.Empty<IChangeSet<int, int>>();
-        var nullChangeSetObs = (IObservable<IChangeSet<int, int>>)null!;
-        var emptyChildChangeSetObs = Observable.Empty<IChangeSet<string, string>>();
-        var emptySelector = new Func<int, IObservable<IChangeSet<string, string>>>(i => emptyChildChangeSetObs);
-        var emptyKeySelector = new Func<int, int, IObservable<IChangeSet<string, string>>>((i, key) => emptyChildChangeSetObs);
-        var nullSelector = (Func<int, IObservable<IChangeSet<string, string>>>)null!;
-        var nullKeySelector = (Func<int, int, IObservable<IChangeSet<string, string>>>)null!;
-        var nullParentComparer = (IComparer<int>)null!;
-        var emptyParentComparer = new NoOpComparer<int>() as IComparer<int>;
-        var nullChildComparer = (IComparer<string>)null!;
-        var emptyChildComparer = new NoOpComparer<string>() as IComparer<string>;
-        var nullEqualityComparer = (IEqualityComparer<string>)null!;
-        var emptyEqualityComparer = new NoOpEqualityComparer<string>() as IEqualityComparer<string>;
-
-        // when
-        var actionDefault1 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector);
-        var actionDefault2a = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector);
-        var actionDefault2b = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector);
-        var actionChildCompare1 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector, comparer: emptyChildComparer);
-        var actionChildCompare2a = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector, comparer: emptyChildComparer);
-        var actionChildCompare2b = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector, comparer: emptyChildComparer);
-        var actionChildCompare2c = () => emptyChangeSetObs.MergeManyChangeSets(emptyKeySelector, comparer: nullChildComparer);
-
-        // then
-        emptyChangeSetObs.Should().NotBeNull();
-        emptyChildChangeSetObs.Should().NotBeNull();
-        emptyChildComparer.Should().NotBeNull();
-        emptyEqualityComparer.Should().NotBeNull();
-        emptyKeySelector.Should().NotBeNull();
-        emptyParentComparer.Should().NotBeNull();
-        emptySelector.Should().NotBeNull();
-        nullChangeSetObs.Should().BeNull();
-        nullChildComparer.Should().BeNull();
-        nullEqualityComparer.Should().BeNull();
-        nullKeySelector.Should().BeNull();
-        nullParentComparer.Should().BeNull();
-        nullSelector.Should().BeNull();
-
-        actionDefault1.Should().Throw<ArgumentNullException>();
-        actionDefault2a.Should().Throw<ArgumentNullException>();
-        actionDefault2b.Should().Throw<ArgumentNullException>();
-        actionChildCompare1.Should().Throw<ArgumentNullException>();
-        actionChildCompare2a.Should().Throw<ArgumentNullException>();
-        actionChildCompare2b.Should().Throw<ArgumentNullException>();
-        actionChildCompare2c.Should().Throw<ArgumentNullException>();
-    }
-
-    [Fact]
-    public void AbleToInvokeFactory()
-    {
-        // having
-        var invoked = false;
-        IObservable<IChangeSet<MarketPrice, int>> factory(IMarket m)
-        {
-            invoked = true;
-            return m.LatestPrices;
-        }
-        using var sub = _marketCache.Connect().MergeManyChangeSets(factory).Subscribe();
-
-        // when
-        _marketCache.AddOrUpdate(new Market(0));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        invoked.Should().BeTrue();
-    }
-
-    [Fact]
-    public void AbleToInvokeFactoryWithKey()
-    {
-        // having
-        var invoked = false;
-        IObservable<IChangeSet<MarketPrice, int>> factory(IMarket m, Guid g)
-        {
-            invoked = true;
-            return m.LatestPrices;
-        }
-        using var sub = _marketCache.Connect().MergeManyChangeSets(factory).Subscribe();
-
-        // when
-        _marketCache.AddOrUpdate(new Market(0));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        invoked.Should().BeTrue();
-    }
-
-    [Fact]
-    public void AllExistingSubItemsPresentInResult()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        AddUniquePrices(markets);
-
-        // when
-        _marketCache.AddOrUpdate(markets);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount);
-        markets.Sum(m => m.PricesCache.Count).Should().Be(MarketCount * PricesPerMarket);
-        results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
-        results.Messages.Count.Should().Be(1);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-    }
-
-    [Fact]
-    public void AllNewSubItemsPresentInResult()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-
-        // when
-        AddUniquePrices(markets);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount);
-        markets.Sum(m => m.PricesCache.Count).Should().Be(MarketCount * PricesPerMarket);
-        results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
-        results.Messages.Count.Should().Be(MarketCount);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-    }
-
-    [Fact]
-    public void AllRefreshedSubItemsAreRefreshed()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-        AddUniquePrices(markets);
-
-        // when
-        markets.ForEach(m => m.RefreshAllPrices(GetRandomPrice));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount);
-        results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
-        results.Messages.Count.Should().Be(MarketCount * 2);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(MarketCount * PricesPerMarket);
-    }
-
-    [Fact]
-    public void AnyDuplicateKeyValuesShouldBeHidden()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-
-        // when
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-    }
-
-    [Fact]
-    public void AnyDuplicateValuesShouldBeNoOpWhenRemoved()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // when
-        markets[1].RemoveAllPrices();
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-    }
-
-    [Fact]
-    public void AnyDuplicateValuesShouldBeUnhiddenWhenOtherIsRemoved()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // when
-        _marketCache.Remove(markets[0]);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Data.Items.Zip(markets[1].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-        results.Messages.Count.Should().Be(2);
-        results.Messages[1].Updates.Should().Be(PricesPerMarket);
-    }
-
-    [Fact]
-    public void AnyDuplicateValuesShouldNotRefreshWhenHidden()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // when
-        markets[1].RefreshAllPrices(GetRandomPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-    }
-
-    [Fact]
-    public void AnyRemovedSubItemIsRemoved()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-        AddUniquePrices(markets);
-
-        // when
-        markets.ForEach(m => m.PricesCache.Edit(updater => updater.RemoveKeys(updater.Keys.Take(RemoveCount))));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount);
-        results.Data.Count.Should().Be(MarketCount * (PricesPerMarket - RemoveCount));
-        results.Messages.Count.Should().Be(MarketCount * 2);
-        results.Messages[0].Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(MarketCount * RemoveCount);
-    }
-
-    [Fact]
-    public void AnySourceItemRemovedRemovesAllSourceValues()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        AddUniquePrices(markets);
-        _marketCache.AddOrUpdate(markets);
-
-        // when
-        _marketCache.Edit(updater => updater.RemoveKeys(updater.Keys.Take(RemoveCount)));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount - RemoveCount);
-        results.Messages.Count.Should().Be(2);
-        results.Data.Count.Should().Be((MarketCount - RemoveCount) * PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(PricesPerMarket * RemoveCount);
-    }
-
-    [Fact]
-    public void ClearingParentEmitsSingleChangeSet()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        AddUniquePrices(markets);
-        _marketCache.AddOrUpdate(markets);
-
-        // when
-        _marketCache.Clear();
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(0);
-        results.Data.Count.Should().Be(0);
-        results.Messages.Count.Should().Be(2);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Updates.Should().Be(0);
-    }
-
-    [Fact]
-    public void ChangingSourceByUpdateRemovesPreviousAndAddsNewValues()
-    {
-        // having
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        var market = new Market(0);
-        market.SetPrices(0, PricesPerMarket * 2, GetRandomPrice);
-        _marketCache.AddOrUpdate(market);
-        var updatedMarket = new Market(market);
-        updatedMarket.SetPrices(PricesPerMarket, PricesPerMarket * 3, GetRandomPrice);
-
-        // when
-        _marketCache.AddOrUpdate(updatedMarket);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        results.Data.Count.Should().Be(PricesPerMarket * 2);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket * 3);
-        results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(PricesPerMarket);
-        results.Data.Items.Zip(updatedMarket.PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-    }
-
-    [Fact]
-    public void ComparerOnlyAddsBetterAddedValues()
-    {
-        // having
-        using var highPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
-        using var lowPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketLow = new Market(1);
-        var marketHigh = new Market(2);
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketLow);
-        _marketCache.AddOrUpdate(marketHigh);
-
-        // when
-        marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
-        marketHigh.SetPrices(0, PricesPerMarket, HighestPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(3);
-        lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
-        highPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketHigh.Id));
-    }
-
-    [Fact]
-    public void ComparerOnlyAddsBetterExistingValues()
-    {
-        // having
-        using var highPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
-        using var lowPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketLow = new Market(1);
-        var marketHigh = new Market(2);
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
-        marketHigh.SetPrices(0, PricesPerMarket, HighestPrice);
-
-        // when
-        _marketCache.AddOrUpdate(marketLow);
-        _marketCache.AddOrUpdate(marketHigh);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(3);
-        lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
-        highPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketHigh.Id));
-    }
-
-    [Fact]
-    public void ComparerOnlyAddsBetterValuesOnSourceUpdate()
-    {
-        // having
-        using var highPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
-        using var lowPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketLow = new Market(1);
-        var marketLowLow = new Market(marketLow);
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
-        marketLowLow.SetPrices(0, PricesPerMarket, LowestPrice - 1);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketLow);
-
-        // when
-        _marketCache.AddOrUpdate(marketLowLow);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLowLow.Id));
-        highPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Removes.Should().Be(0);
-        highPriceResults.Summary.Overall.Updates.Should().Be(0);
-        highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-    }
-
-    [Fact]
-    public void ComparerUpdatesToCorrectValueOnRefresh()
-    {
-        // having
-        using var highPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
-        using var lowPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketFlipFlop = new Market(1);
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketFlipFlop.SetPrices(0, PricesPerMarket, HighestPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketFlipFlop);
-
-        // when
-        marketFlipFlop.RefreshAllPrices(LowestPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketFlipFlop.Id));
-        highPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Removes.Should().Be(0);
-        highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        highPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-    }
-
-    [Fact]
-    public void ComparerUpdatesToCorrectValueOnRemove()
-    {
-        // having
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        using var lowPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
-        using var highPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketLow = new Market(1);
-        var marketHigh = new Market(2);
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketLow);
-        _marketCache.AddOrUpdate(marketHigh);
-        marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
-        marketHigh.SetPrices(0, PricesPerMarket, HighestPrice);
-
-        // when
-        _marketCache.Remove(marketLow);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-        lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-        highPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Removes.Should().Be(0);
-        highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketHigh.Id));
-    }
-
-    [Fact]
-    public void ComparerUpdatesToCorrectValueOnUpdate()
-    {
-        // having
-        using var highPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
-        using var lowPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketFlipFlop = new Market(1);
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketFlipFlop.SetPrices(0, PricesPerMarket, HighestPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketFlipFlop);
-
-        // when
-        marketFlipFlop.UpdateAllPrices(LowestPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketFlipFlop.Id));
-        highPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Removes.Should().Be(0);
-        highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        highPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-    }
-
-    [Fact]
-    public void ComparerOnlyUpdatesVisibleValuesOnUpdate()
-    {
-        // having
-        using var highPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
-        using var lowPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketLow = new Market(1);
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketLow);
-
-        // when
-        marketLow.UpdateAllPrices(LowestPrice - 1);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        lowPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
-        highPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Removes.Should().Be(0);
-        highPriceResults.Summary.Overall.Updates.Should().Be(0);
-        highPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-    }
-
-    [Fact]
-    public void ComparerOnlyRefreshesVisibleValues()
-    {
-        // having
-        using var highPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer, MarketPrice.HighPriceCompare).AsAggregator();
-        using var lowPriceResults = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer, MarketPrice.LowPriceCompare).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketLow = new Market(1);
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketLow);
-
-        // when
-        marketLow.RefreshAllPrices(LowestPrice - 1);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        lowPriceResults.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
-        lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
-        highPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        highPriceResults.Summary.Overall.Removes.Should().Be(0);
-        highPriceResults.Summary.Overall.Updates.Should().Be(0);
-        highPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-    }
-
-    [Fact]
-    public void EqualityComparerHidesUpdatesWithoutChanges()
-    {
-        // having
-        var market = new Market(0);
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        market.SetPrices(0, PricesPerMarket, LowestPrice);
-        _marketCache.AddOrUpdate(market);
-
-        // when
-        market.SetPrices(0, PricesPerMarket, LowestPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Messages.Count.Should().Be(1);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void EveryItemVisibleWhenSequenceCompletes()
-    {
-        // having
-        _marketCache.AddOrUpdate(Enumerable.Range(0, MarketCount).Select(n => new FixedMarket(GetRandomPrice, n * ItemIdStride, (n * ItemIdStride) + PricesPerMarket)));
-
-        // when
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices).AsAggregator();
-        DisposeMarkets();
-
-        // then
-        results.Data.Count.Should().Be(PricesPerMarket * MarketCount);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket * MarketCount);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Theory]
-    [InlineData(false, false)]
-    [InlineData(false, true)]
-    [InlineData(true, false)]
-    [InlineData(true, true)]
-    public void MergedObservableCompletesOnlyWhenSourceAndAllChildrenComplete(bool completeSource, bool completeChildren)
-    {
-        // having
-        _marketCache.AddOrUpdate(Enumerable.Range(0, MarketCount).Select(n => new FixedMarket(GetRandomPrice, n * ItemIdStride, (n * ItemIdStride) + PricesPerMarket, completable: completeChildren)));
-        var hasSourceSequenceCompleted = false;
-        var hasMergedSequenceCompleted = false;
-
-        using var cleanup = _marketCache.Connect().Do(_ => { }, () => hasSourceSequenceCompleted = true)
-                            .MergeManyChangeSets(m => m.LatestPrices).Subscribe(_ => { }, () => hasMergedSequenceCompleted = true);
-
-        // when
-        if (completeSource)
-        {
-            DisposeMarkets();
-        }
-
-        // then
-        hasSourceSequenceCompleted.Should().Be(completeSource);
-        hasMergedSequenceCompleted.Should().Be(completeSource && completeChildren);
-    }
-
-    [Fact]
-    public void MergedObservableWillFailIfSourceFails()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        _marketCache.AddOrUpdate(markets);
-        var receivedError = default(Exception);
-        var expectedError = new Exception("Test exception");
-        var throwObservable = Observable.Throw<IChangeSet<IMarket, Guid>>(expectedError);
-
-        using var cleanup = _marketCache.Connect().Concat(throwObservable)
-                            .MergeManyChangeSets(m => m.LatestPrices).Subscribe(_ => { }, err => receivedError = err);
-
-        // when
-        DisposeMarkets();
-
-        // then
-        receivedError.Should().Be(expectedError);
-    }
-
-    [Fact]
-    public void MergeManyChangeSetsWorksCorrectlyWithValueTypes()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        _marketCache.AddOrUpdate(markets);
-        markets.ForEach(m => m.SetPrices(0, PricesPerMarket, GetRandomPrice));
-        using var results = _marketCache.Connect()
-                .MergeManyChangeSets(m => m.LatestPrices.Transform(p => p.Price))
-                .AsAggregator();
-
-        // when
-        markets.ForEach(m => m.RemoveAllPrices());
-
-        // then
-        results.Data.Count.Should().Be(0);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(PricesPerMarket);
-    }
-
-
-    [Theory]
-    [InlineData(true)]
-    [InlineData(false)]
-    public void OrderOfChangesIsPreserved(bool removeFirst)
-    {
-        // Arrange
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        AddUniquePrices(markets);
-        _marketCache.AddOrUpdate(markets);
-        var markets2 = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        AddUniquePrices(markets2);
-        using var results = _marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
-        (var firstReason, var nextReason, int expectedChanges) = removeFirst 
-            ? (ChangeReason.Remove, ChangeReason.Add, 2 * MarketCount * PricesPerMarket)
-            : (ChangeReason.Add, ChangeReason.Remove, 3 * MarketCount * PricesPerMarket);
-
-        // Act
-        _marketCache.Edit(updater =>
-        {
-            if (removeFirst)
-            {
-                updater.Clear();
-                updater.AddOrUpdate(markets2);
-            }
-            else
-            {
-
-                updater.AddOrUpdate(markets2);
-                updater.Clear();
-            }
-        });
-
-        // Assert
-        results.Messages.Count.Should().Be(2);
-        results.Messages[0].All(change => change.Reason is ChangeReason.Add).Should().BeTrue();
-        results.Messages[1].Count.Should().Be(expectedChanges);
-        results.Messages[1].Take(MarketCount * PricesPerMarket).All(change => change.Reason == firstReason).Should().BeTrue();
-        results.Messages[1].Skip(MarketCount * PricesPerMarket).All(change => change.Reason == nextReason).Should().BeTrue();
-    }
-
-    public void Dispose()
-    {
-        _marketCacheResults.Dispose();
-        DisposeMarkets();
-    }
-
-    private void AddUniquePrices(Market[] markets) => markets.ForEach(m => m.AddUniquePrices(PricesPerMarket, _ => GetRandomPrice()));
-
-    private void CheckResultContents(ChangeSetAggregator<IMarket, Guid> marketResults, ChangeSetAggregator<MarketPrice, int> priceResults)
-    {
-        var expectedMarkets = _marketCache.Items.ToList();
-        var expectedPrices = expectedMarkets.SelectMany(market => ((Market)market).PricesCache.Items).ToList();
-
-        // These should be subsets of each other
-        expectedMarkets.Should().BeSubsetOf(marketResults.Data.Items);
-        marketResults.Data.Items.Count.Should().Be(expectedMarkets.Count);
-
-        // These should be subsets of each other
-        expectedPrices.Should().BeSubsetOf(priceResults.Data.Items);
-        priceResults.Data.Items.Count.Should().Be(expectedPrices.Count);
-    }
-
-    private void DisposeMarkets()
-    {
-        _marketCache.Items.ForEach(m => (m as IDisposable)?.Dispose());
-        _marketCache.Dispose();
-        _marketCache.Clear();
-    }
-
-    private decimal GetRandomPrice() => MarketPrice.RandomPrice(_randomizer, BasePrice, PriceOffset);
-}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheSourceCompareFixture.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheSourceCompareFixture.cs
deleted file mode 100644
index ce6cc89fd..000000000
--- a/src/DynamicData.Tests/Cache/MergeManyChangeSetsCacheSourceCompareFixture.cs
+++ /dev/null
@@ -1,1105 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Reactive.Concurrency;
-using System.Reactive.Disposables;
-using System.Reactive;
-using System.Reactive.Linq;
-using System.Reactive.Threading.Tasks;
-using System.Threading.Tasks;
-using Bogus;
-using DynamicData.Kernel;
-using DynamicData.Tests.Domain;
-using DynamicData.Tests.Utilities;
-using FluentAssertions;
-
-using Xunit;
-
-namespace DynamicData.Tests.Cache;
-
-public sealed class MergeManyChangeSetsCacheSourceCompareFixture : IDisposable
-{
-#if DEBUG
-    const int MarketCount = 5;
-    const int PricesPerMarket = 7;
-    const int RemoveCount = 3;
-#else
-    const int MarketCount = 101;
-    const int PricesPerMarket = 103;
-    const int RemoveCount = 53;
-#endif
-
-    const int ItemIdStride = 1000;
-    const decimal BasePrice = 10m;
-    const decimal PriceOffset = 10m;
-    const decimal HighestPrice = BasePrice + PriceOffset + 1.0m;
-    const decimal LowestPrice = BasePrice - 1.0m;
-
-    private readonly ISourceCache<IMarket, Guid> _marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
-
-    private readonly ChangeSetAggregator<IMarket, Guid> _marketCacheResults;
-
-    private readonly Faker<Market> _marketFaker;
-
-    private readonly Randomizer _randomizer;
-
-    public MergeManyChangeSetsCacheSourceCompareFixture()
-    {
-        _randomizer = new(0x10012022);
-        _marketFaker = Fakers.Market.RuleFor(m => m.Rating, faker => faker.Random.Double(0, 5)).WithSeed(_randomizer);
-        _marketCacheResults = _marketCache.Connect().AsAggregator();
-    }
-
-    [Theory]
-    [InlineData(5, 7)]
-    [InlineData(10, 50)]
-#if false && !DEBUG
-    [InlineData(100, 100)]
-    [InlineData(10, 1_000)]
-    [InlineData(1_000, 10)]
-#endif
-    public async Task MultiThreadedStressTest(int marketCount, int priceCount)
-    {
-        const int MaxItemId = 50;
-        var MaxAddTime = TimeSpan.FromSeconds(0.250);
-        var MaxRemoveTime = TimeSpan.FromSeconds(0.100);
-
-        TimeSpan? GetRemoveTime() => _randomizer.Bool() ? _randomizer.TimeSpan(MaxRemoveTime) : null;
-
-        IObservable<Unit> AddRemoveStress(int marketCount, int priceCount, int parallel, IScheduler scheduler) =>
-            Observable.Create<Unit>(observer => new CompositeDisposable
-                {
-                    AddRemoveMarkets(marketCount, parallel, scheduler)
-                            .Subscribe(
-                                onNext: static _ => { },
-                                onError: observer.OnError),
-                    _marketCache.Connect()
-                            .MergeMany(market => AddRemovePrices((Market)market, priceCount, parallel, scheduler))
-                            .Subscribe(
-                                onNext: static _ => { },
-                                onError: observer.OnError,
-                                onCompleted: observer.OnCompleted)
-                });
-
-        IObservable<IMarket> AddRemoveMarkets(int ownerCount, int parallel, IScheduler scheduler) =>
-            _marketFaker.IntervalGenerate(MaxAddTime, scheduler)
-                .Parallelize(ownerCount, parallel, obs => obs.StressAddRemove(_marketCache, _ => GetRemoveTime(), scheduler))
-                .Finally(_marketCache.Dispose);
-
-        IObservable<MarketPrice> AddRemovePrices(Market market, int priceCount, int parallel, IScheduler scheduler) =>
-            _randomizer.Interval(MaxAddTime, scheduler).Select(_ => market.CreatePrice(_randomizer.Number(MaxItemId), GetRandomPrice()))
-                .Parallelize(priceCount, parallel, obs => obs.StressAddRemove(market.PricesCache, _ => GetRemoveTime(), scheduler))
-                .Finally(market.PricesCache.Dispose);
-
-        var merged = _marketCache.Connect().MergeManyChangeSets(market => market.LatestPrices, Market.RatingCompare, resortOnSourceRefresh: true).Publish();
-        var adding = true;
-        var cacheCompleted = merged.LastOrDefaultAsync().ToTask();
-        using var priceResults = merged.AsAggregator();
-        using var connect = merged.Connect();
-
-        // Start asynchrononously modifying the parent list and the child lists
-        using var addingSub = AddRemoveStress(marketCount, priceCount, Environment.ProcessorCount, TaskPoolScheduler.Default)
-            .Finally(() => adding = false)
-            .Subscribe();
-
-        // Subscribe / unsubscribe over and over while the collections are being modified
-        do
-        {
-            // Ensure items are being added asynchronously before subscribing to changes
-            await Task.Yield();
-
-            {
-                // Subscribe
-                var mergedSub = merged.Subscribe();
-
-                // Let other threads run
-                await Task.Yield();
-
-                // Unsubscribe
-                mergedSub.Dispose();
-            }
-        }
-        while (adding);
-
-        // Wait for the source cache to finish delivering all notifications.
-        await cacheCompleted;
-
-        // Verify the results
-        CheckResultContents(_marketCacheResults, priceResults, Market.RatingCompare);
-    }
-
-    [Fact]
-    public void NullChecks()
-    {
-        // having
-        var emptyChangeSetObs = Observable.Empty<IChangeSet<int, int>>();
-        var nullChangeSetObs = (IObservable<IChangeSet<int, int>>)null!;
-        var emptyChildChangeSetObs = Observable.Empty<IChangeSet<string, string>>();
-        var emptySelector = new Func<int, IObservable<IChangeSet<string, string>>>(i => emptyChildChangeSetObs);
-        var emptyKeySelector = new Func<int, int, IObservable<IChangeSet<string, string>>>((i, key) => emptyChildChangeSetObs);
-        var nullSelector = (Func<int, IObservable<IChangeSet<string, string>>>)null!;
-        var nullKeySelector = (Func<int, int, IObservable<IChangeSet<string, string>>>)null!;
-        var nullParentComparer = (IComparer<int>)null!;
-        var emptyParentComparer = new NoOpComparer<int>() as IComparer<int>;
-        var nullChildComparer = (IComparer<string>)null!;
-        var emptyChildComparer = new NoOpComparer<string>() as IComparer<string>;
-        var nullEqualityComparer = (IEqualityComparer<string>)null!;
-        var emptyEqualityComparer = new NoOpEqualityComparer<string>() as IEqualityComparer<string>;
-
-        // when
-        var actionParentCompare1 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector, sourceComparer: emptyParentComparer);
-        var actionParentCompareKey1a = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector, sourceComparer: emptyParentComparer);
-        var actionParentCompareKey1b = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector, sourceComparer: emptyParentComparer);
-        var actionParentCompareKey1c = () => emptyChangeSetObs.MergeManyChangeSets(emptyKeySelector, sourceComparer: nullParentComparer);
-        var actionParentCompare2 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector, sourceComparer: emptyParentComparer, equalityComparer: emptyEqualityComparer);
-        var actionParentCompareKey2a = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector, sourceComparer: emptyParentComparer, equalityComparer: emptyEqualityComparer);
-        var actionParentCompareKey2b = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector, sourceComparer: emptyParentComparer, equalityComparer: emptyEqualityComparer);
-
-        // then
-        emptyChangeSetObs.Should().NotBeNull();
-        emptyChildChangeSetObs.Should().NotBeNull();
-        emptyChildComparer.Should().NotBeNull();
-        emptyEqualityComparer.Should().NotBeNull();
-        emptyKeySelector.Should().NotBeNull();
-        emptyParentComparer.Should().NotBeNull();
-        emptySelector.Should().NotBeNull();
-        nullChangeSetObs.Should().BeNull();
-        nullChildComparer.Should().BeNull();
-        nullEqualityComparer.Should().BeNull();
-        nullKeySelector.Should().BeNull();
-        nullParentComparer.Should().BeNull();
-        nullSelector.Should().BeNull();
-
-        actionParentCompare1.Should().Throw<ArgumentNullException>();
-        actionParentCompareKey1a.Should().Throw<ArgumentNullException>();
-        actionParentCompareKey1b.Should().Throw<ArgumentNullException>();
-        actionParentCompareKey1c.Should().Throw<ArgumentNullException>();
-        actionParentCompare2.Should().Throw<ArgumentNullException>();
-        actionParentCompareKey2a.Should().Throw<ArgumentNullException>();
-        actionParentCompareKey2b.Should().Throw<ArgumentNullException>();
-    }
-
-    [Fact]
-    public void AbleToInvokeFactory()
-    {
-        // having
-        var invoked = false;
-        IObservable<IChangeSet<MarketPrice, int>> factory(IMarket m)
-        {
-            invoked = true;
-            return m.LatestPrices;
-        }
-        using var sub = _marketCache.Connect().MergeManyChangeSets(factory, Market.RatingCompare).Subscribe();
-
-        // when
-        _marketCache.AddOrUpdate(new Market(0));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        invoked.Should().BeTrue();
-    }
-
-    [Fact]
-    public void AbleToInvokeFactoryWithKey()
-    {
-        // having
-        var invoked = false;
-        IObservable<IChangeSet<MarketPrice, int>> factory(IMarket m, Guid g)
-        {
-            invoked = true;
-            return m.LatestPrices;
-        }
-        using var sub = _marketCache.Connect().MergeManyChangeSets(factory, Market.RatingCompare).Subscribe();
-
-        // when
-        _marketCache.AddOrUpdate(new Market(0));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        invoked.Should().BeTrue();
-    }
-
-    [Fact]
-    public void AllExistingSubItemsPresentInResult()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, GetRandomPrice));
-
-        // when
-        _marketCache.AddOrUpdate(markets);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount);
-        markets.Sum(m => m.PricesCache.Count).Should().Be(MarketCount * PricesPerMarket);
-        results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
-        results.Messages.Count.Should().Be(1);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void AllNewSubItemsPresentInResult()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-
-        // when
-        markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, GetRandomPrice));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount);
-        markets.Sum(m => m.PricesCache.Count).Should().Be(MarketCount * PricesPerMarket);
-        results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
-        results.Messages.Count.Should().Be(MarketCount);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void AllRefreshedSubItemsAreRefreshed()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, GetRandomPrice));
-        _marketCache.AddOrUpdate(markets);
-
-        // when
-        markets.ForEach(m => m.RefreshAllPrices(GetRandomPrice));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount);
-        results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
-        results.Messages.Count.Should().Be(MarketCount + 1);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(MarketCount * PricesPerMarket);
-    }
-
-    [Fact]
-    public void AnyDuplicateKeyValuesShouldBeHidden()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        markets[0].Rating = 1.0;
-        _marketCache.AddOrUpdate(markets);
-
-        // when
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void AnyDuplicateValuesShouldBeNoOpWhenRemoved()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        markets[0].Rating = 1.0;
-        _marketCache.AddOrUpdate(markets);
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // when
-        markets[1].RemoveAllPrices();
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void AnyDuplicateValuesShouldBeUnhiddenWhenOtherIsRemoved()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        markets[0].Rating = 1.0;
-        _marketCache.AddOrUpdate(markets);
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // when
-        _marketCache.Remove(markets[0]);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Data.Items.Zip(markets[1].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-        results.Messages.Count.Should().Be(2);
-        results.Messages[1].Updates.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void AnyDuplicateValuesShouldNotRefreshWhenHidden()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        markets[0].Rating = 1.0;
-        _marketCache.AddOrUpdate(markets);
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // when
-        markets[1].RefreshAllPrices(GetRandomPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void SourceRefreshGeneratesUpdatesAsNeeded()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        markets[0].Rating = 1.0;
-        _marketCache.AddOrUpdate(markets);
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // when
-        SetRating(markets[1], 2.0);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Data.Items.Zip(markets[1].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void SourceRefreshDoesNothingIfDisabled()
-    {
-        // having
-        var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating(resortOnRefresh: false).AsAggregator();
-        markets[0].Rating = 1.0;
-        _marketCache.AddOrUpdate(markets);
-        markets[0].SetPrices(0, PricesPerMarket, GetRandomPrice);
-        markets[1].SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // when
-        SetRating(markets[1], 2.0);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void AnyRemovedSubItemIsRemoved()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-        markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, GetRandomPrice));
-
-        // when
-        markets.ForEach(m => m.PricesCache.Edit(updater => updater.RemoveKeys(updater.Keys.Take(RemoveCount))));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount);
-        results.Data.Count.Should().Be(MarketCount * (PricesPerMarket - RemoveCount));
-        results.Messages.Count.Should().Be(MarketCount * 2);
-        results.Messages[0].Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(MarketCount * RemoveCount);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void AnySourceItemRemovedRemovesAllSourceValues()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        using var results = ChangeSetByRating().AsAggregator();
-        _marketCache.AddOrUpdate(markets);
-        markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, GetRandomPrice));
-
-        // when
-        _marketCache.Edit(updater => updater.RemoveKeys(updater.Keys.Take(RemoveCount)));
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(MarketCount - RemoveCount);
-        results.Data.Count.Should().Be((MarketCount - RemoveCount) * PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(PricesPerMarket * RemoveCount);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void ChangingSourceByUpdateRemovesPreviousAndAddsNewValues()
-    {
-        // having
-        using var results = ChangeSetByRating(false).AsAggregator();
-        var market = new Market(0);
-        market.SetPrices(0, PricesPerMarket * 2, GetRandomPrice);
-        _marketCache.AddOrUpdate(market);
-        var updatedMarket = new Market(market);
-        updatedMarket.SetPrices(PricesPerMarket, PricesPerMarket * 3, GetRandomPrice);
-
-        // when
-        _marketCache.AddOrUpdate(updatedMarket);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        results.Data.Count.Should().Be(PricesPerMarket * 2);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket * 3);
-        results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Zip(updatedMarket.PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
-    }
-
-    [Fact]
-    public void ChangingSourceByUpdateRemovesPreviousAndEmitsBetterValues()
-    {
-        // having
-        using var results = ChangeSetByRating(false).AsAggregator();
-        var market = new Market(0);
-        var marketWorse = new Market(1);
-        SetRating(marketWorse, -1);
-        market.SetPrices(0, PricesPerMarket * 2, GetRandomPrice);
-        marketWorse.SetPrices(0, PricesPerMarket * 2, GetRandomPrice);
-        _marketCache.AddOrUpdate(market);
-        _marketCache.AddOrUpdate(marketWorse);
-
-        var updatedMarket = new Market(market);
-        updatedMarket.SetPrices(PricesPerMarket, PricesPerMarket * 3, GetRandomPrice);
-
-        // when
-        _marketCache.AddOrUpdate(updatedMarket);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket * 3);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket * 3);
-        results.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Take(PricesPerMarket).Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketWorse.Id));
-        results.Data.Items.Skip(PricesPerMarket).Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(updatedMarket.Id));
-    }
-
-    [Fact]
-    public void UpdatesToCorrectValueOnRemove()
-    {
-        // having
-        var marketOriginal = new Market(0);
-        var marketBetter = new Market(1);
-        var marketBest = new Market(2);
-        marketBetter.Rating = 1.0;
-        marketBest.Rating = 5.0;
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketBetter.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketBest.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketBest);
-        _marketCache.AddOrUpdate(marketBetter);
-        using var results = ChangeSetByRating(false).AsAggregator();
-
-        // when
-        _marketCache.Remove(marketBest);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
-    }
-
-    [Fact]
-    public void OnlyUpdatesOnDuplicateIfNewItemIsFromBetterParent()
-    {
-        // having
-        using var results = ChangeSetByRating(false).AsAggregator();
-        using var resultsLow = ChangeSetByLowRating(false).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketBetter = new Market(1);
-        marketBetter.Rating = 1.0;
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketBetter.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-
-        // when
-        _marketCache.AddOrUpdate(marketBetter);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
-        resultsLow.Data.Count.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Updates.Should().Be(0);
-        resultsLow.Summary.Overall.Removes.Should().Be(0);
-        resultsLow.Summary.Overall.Refreshes.Should().Be(0);
-        resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-    }
-
-    [Fact]
-    public void BestChoiceFromDuplicatesSelectedWhenChangeSetCreated()
-    {
-        // having
-        var marketOriginal = new Market(0);
-        var marketBetter = new Market(1);
-        marketBetter.Rating = 1.0;
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketBetter.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketBetter);
-
-        // when
-        using var results = ChangeSetByRating(false).AsAggregator();
-        using var resultsLow = ChangeSetByLowRating(false).AsAggregator();
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
-        resultsLow.Data.Count.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Updates.Should().Be(0);
-        resultsLow.Summary.Overall.Removes.Should().Be(0);
-        resultsLow.Summary.Overall.Refreshes.Should().Be(0);
-        resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-    }
-
-    [Fact]
-    public void OnlyAddsBetterValuesOnSourceUpdate()
-    {
-        // having
-        using var results = ChangeSetByRating(false).AsAggregator();
-        using var resultsLow = ChangeSetByLowRating(false).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketBetter = new Market(1);
-        marketBetter.Rating = 1.0;
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketBetter);
-
-        // when
-        marketBetter.SetPrices(0, PricesPerMarket, GetRandomPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
-        resultsLow.Data.Count.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Updates.Should().Be(0);
-        resultsLow.Summary.Overall.Removes.Should().Be(0);
-        resultsLow.Summary.Overall.Refreshes.Should().Be(0);
-        resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-    }
-
-    [Fact]
-    public void UpdatesToCorrectValueOnRefresh()
-    {
-        // having
-        using var results = ChangeSetByRating(false).AsAggregator();
-        using var resultsLow = ChangeSetByLowRating(false).AsAggregator();
-        using var resultsRefresh = ChangeSetByRating(true).AsAggregator();
-        using var resultsLowRefresh = ChangeSetByLowRating(true).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketBetter = new Market(1);
-        marketBetter.Rating = -1.0;
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketBetter.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketBetter);
-
-        // when
-        SetRating(marketBetter, 2.0);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        _marketCacheResults.Summary.Overall.Refreshes.Should().Be(1);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-        resultsLow.Data.Count.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Removes.Should().Be(0);
-        resultsLow.Summary.Overall.Refreshes.Should().Be(0);
-        resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
-        resultsRefresh.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsRefresh.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        resultsRefresh.Summary.Overall.Removes.Should().Be(0);
-        resultsRefresh.Summary.Overall.Refreshes.Should().Be(0);
-        resultsRefresh.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
-        resultsLowRefresh.Data.Count.Should().Be(PricesPerMarket);
-        resultsLowRefresh.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLowRefresh.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        resultsLowRefresh.Summary.Overall.Removes.Should().Be(0);
-        resultsLowRefresh.Summary.Overall.Refreshes.Should().Be(0);
-        resultsLowRefresh.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-    }
-
-    [Fact]
-    public void ChildComparerUpdatesToCorrectValueOnUpdate()
-    {
-        // having
-        using var resultsLow = ChangeSetByLowRating(false).AsAggregator();
-        using var resultsLowPrice = ChangeSetByRatingThenLowPrice(false).AsAggregator();
-        using var resultsHighPrice = ChangeSetByRatingThenHighPrice(false).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketHighest = new Market(1);
-        var marketLowest = new Market(2);
-        marketLowest.Rating = marketHighest.Rating = 1.0;
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketHighest.SetPrices(0, PricesPerMarket, HighestPrice);
-        marketLowest.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketHighest);
-        _marketCache.AddOrUpdate(marketLowest);
-
-        // when
-        marketLowest.UpdateAllPrices(LowestPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(3);
-        resultsLow.Data.Count.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Updates.Should().Be(0);
-        resultsLow.Summary.Overall.Removes.Should().Be(0);
-        resultsLow.Summary.Overall.Refreshes.Should().Be(0);
-        resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-
-        resultsLowPrice.Data.Count.Should().Be(PricesPerMarket);
-        resultsLowPrice.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLowPrice.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
-        resultsLowPrice.Summary.Overall.Removes.Should().Be(0);
-        resultsLowPrice.Summary.Overall.Refreshes.Should().Be(0);
-        resultsLowPrice.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLowest.Id));
-
-        resultsHighPrice.Data.Count.Should().Be(PricesPerMarket);
-        resultsHighPrice.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsHighPrice.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        resultsHighPrice.Summary.Overall.Removes.Should().Be(0);
-        resultsHighPrice.Summary.Overall.Refreshes.Should().Be(0);
-        resultsHighPrice.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketHighest.Id));
-    }
-
-    [Fact]
-    public void ChildComparerOnlyUpdatesVisibleValuesOnUpdate()
-    {
-        // having
-        using var results = ChangeSetByRating(false).AsAggregator();
-        using var lowRatingLowPriceResults = ChangeSetByLowRatingThenLowPrice(false).AsAggregator();
-        using var lowRatingHighPriceResults = ChangeSetByLowRatingThenHighPrice(false).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketLow = new Market(1);
-        var marketLowest = new Market(2);
-
-        marketLowest.Rating = marketLow.Rating = -1;
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
-        marketLowest.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketLow);
-        _marketCache.AddOrUpdate(marketLowest);
-
-        // when
-        marketLowest.UpdateAllPrices(LowestPrice - 1);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(3);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-        lowRatingLowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowRatingLowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowRatingLowPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowRatingLowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        lowRatingLowPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        lowRatingLowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLowest.Id));
-        lowRatingHighPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowRatingHighPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowRatingHighPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowRatingHighPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
-        lowRatingHighPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        lowRatingHighPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
-    }
-
-    [Fact]
-    public void ChildComparerOnlyRefreshesVisibleValues()
-    {
-        // having
-        using var results = ChangeSetByRating(false).AsAggregator();
-        using var lowRatingLowPriceResults = ChangeSetByLowRatingThenLowPrice(false).AsAggregator();
-        using var lowRatingHighPriceResults = ChangeSetByLowRatingThenHighPrice(false).AsAggregator();
-        var marketOriginal = new Market(0);
-        var marketLow = new Market(1);
-        var marketLowest = new Market(2);
-
-        marketLowest.Rating = marketLow.Rating = -1;
-        marketOriginal.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketLow.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        marketLowest.SetPrices(0, PricesPerMarket, LowestPrice);
-        _marketCache.AddOrUpdate(marketOriginal);
-        _marketCache.AddOrUpdate(marketLow);
-        _marketCache.AddOrUpdate(marketLowest);
-
-        // when
-        marketLowest.RefreshAllPrices(LowestPrice - 1);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(3);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-        results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
-        lowRatingLowPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowRatingLowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowRatingLowPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowRatingLowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        lowRatingLowPriceResults.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
-        lowRatingLowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLowest.Id));
-        lowRatingHighPriceResults.Data.Count.Should().Be(PricesPerMarket);
-        lowRatingHighPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        lowRatingHighPriceResults.Summary.Overall.Removes.Should().Be(0);
-        lowRatingHighPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
-        lowRatingHighPriceResults.Summary.Overall.Refreshes.Should().Be(0);
-        lowRatingHighPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
-    }
-
-    [Fact]
-    public void EqualityComparerHidesUpdatesWithoutChanges()
-    {
-        // having
-        var market = new Market(0);
-        using var results = CreateChangeSet("Equality Compare", Market.RatingCompare, equalityComparer: MarketPrice.EqualityComparer, resortOnRefresh: true).AsAggregator();
-        market.SetPrices(0, PricesPerMarket, LowestPrice);
-        _marketCache.AddOrUpdate(market);
-
-        // when
-        market.SetPrices(0, PricesPerMarket, LowestPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(1);
-        results.Data.Count.Should().Be(PricesPerMarket);
-        results.Messages.Count.Should().Be(1);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void EqualityComparerAndChildComparerWorkTogetherForUpdates()
-    {
-        // having
-        using var resultsLow = ChangeSetByLowRating().AsAggregator();
-        using var resultsRecent = ChangeSetByRatingThenRecent().AsAggregator();
-        using var resultsTimeStamp = ChangeSetByRatingThenTimeStamp().AsAggregator();
-        var marketLow = new Market(0);
-        var market = new Market(1);
-        marketLow.Rating = -1;
-        marketLow.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        market.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketLow);
-        _marketCache.AddOrUpdate(market);
-        market.SetPrices(0, PricesPerMarket, LowestPrice);
-
-        // when
-        market.UpdateAllPrices(LowestPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        resultsLow.Data.Count.Should().Be(PricesPerMarket);
-        resultsLow.Messages.Count.Should().Be(1);
-        resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Removes.Should().Be(0);
-        resultsLow.Summary.Overall.Updates.Should().Be(0);
-        resultsLow.Summary.Overall.Refreshes.Should().Be(0);
-        resultsRecent.Messages.Count.Should().Be(3);
-        resultsRecent.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsRecent.Summary.Overall.Removes.Should().Be(0);
-        resultsRecent.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        resultsRecent.Summary.Overall.Refreshes.Should().Be(0);
-        resultsTimeStamp.Messages.Count.Should().Be(4);
-        resultsTimeStamp.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsTimeStamp.Summary.Overall.Removes.Should().Be(0);
-        resultsTimeStamp.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
-        resultsTimeStamp.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Fact]
-    public void EqualityComparerAndChildComparerWorkTogetherForRefreshes()
-    {
-        // having
-        using var resultsLow = ChangeSetByLowRating().AsAggregator();
-        using var resultsRecent = ChangeSetByRatingThenRecent().AsAggregator();
-        using var resultsTimeStamp = ChangeSetByRatingThenTimeStamp().AsAggregator();
-        var marketLow = new Market(0);
-        var market = new Market(1);
-        marketLow.Rating = -1;
-        marketLow.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        market.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketLow);
-        _marketCache.AddOrUpdate(market);
-        market.SetPrices(0, PricesPerMarket, LowestPrice);
-        // Update again, but only the timestamp will change, so resultsRecent will ignore
-        market.SetPrices(0, PricesPerMarket, LowestPrice);
-
-        // when
-        // resultsRecent won't see the refresh because it ignored the update
-        // resultsTimeStamp will see the refreshes because it didn't
-        market.RefreshAllPrices(LowestPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        resultsLow.Data.Count.Should().Be(PricesPerMarket);
-        resultsLow.Messages.Count.Should().Be(1);
-        resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Removes.Should().Be(0);
-        resultsLow.Summary.Overall.Updates.Should().Be(0);
-        resultsLow.Summary.Overall.Refreshes.Should().Be(0);
-        resultsRecent.Messages.Count.Should().Be(4);
-        resultsRecent.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsRecent.Summary.Overall.Removes.Should().Be(0);
-        resultsRecent.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
-        resultsRecent.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
-        resultsTimeStamp.Messages.Count.Should().Be(5);
-        resultsTimeStamp.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsTimeStamp.Summary.Overall.Removes.Should().Be(0);
-        resultsTimeStamp.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
-        resultsTimeStamp.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
-    }
-
-    [Fact]
-    public void EqualityComparerAndChildComparerRefreshesBecomeUpdates()
-    {
-        // having
-        using var resultsLow = ChangeSetByLowRating().AsAggregator();
-        using var resultsRecent = ChangeSetByRatingThenRecent().AsAggregator();
-        using var resultsTimeStamp = ChangeSetByRatingThenTimeStamp().AsAggregator();
-        var marketLow = new Market(0);
-        var market = new Market(1);
-        marketLow.Rating = -1;
-        marketLow.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        market.SetPrices(0, PricesPerMarket, GetRandomPrice);
-        _marketCache.AddOrUpdate(marketLow);
-        _marketCache.AddOrUpdate(market);
-        market.SetPrices(0, PricesPerMarket, LowestPrice);
-        // Update again, but only the timestamp will change, so resultsRecent will ignore
-        market.SetPrices(0, PricesPerMarket, LowestPrice);
-
-        // when
-        // resultsRecent won't see the refresh because it ignored the update
-        // resultsTimeStamp will see the refreshes because it didn't
-        market.RefreshAllPrices(GetRandomPrice);
-
-        // then
-        _marketCacheResults.Data.Count.Should().Be(2);
-        resultsLow.Data.Count.Should().Be(PricesPerMarket);
-        resultsLow.Messages.Count.Should().Be(1);
-        resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsLow.Summary.Overall.Removes.Should().Be(0);
-        resultsLow.Summary.Overall.Updates.Should().Be(0);
-        resultsLow.Summary.Overall.Refreshes.Should().Be(0);
-        resultsRecent.Messages.Count.Should().Be(4);
-        resultsRecent.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsRecent.Summary.Overall.Removes.Should().Be(0);
-        resultsRecent.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
-        resultsRecent.Summary.Overall.Refreshes.Should().Be(0);
-        resultsTimeStamp.Messages.Count.Should().Be(5);
-        resultsTimeStamp.Summary.Overall.Adds.Should().Be(PricesPerMarket);
-        resultsTimeStamp.Summary.Overall.Removes.Should().Be(0);
-        resultsTimeStamp.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
-        resultsTimeStamp.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
-    }
-
-    [Fact]
-    public void EveryItemVisibleWhenSequenceCompletes()
-    {
-        // having
-        _marketCache.AddOrUpdate(Enumerable.Range(0, MarketCount).Select(n => new FixedMarket(GetRandomPrice, n * ItemIdStride, (n * ItemIdStride) + PricesPerMarket)));
-
-        // when
-        using var results = ChangeSetByRating(false).AsAggregator();
-        DisposeMarkets();
-
-        // then
-        results.Data.Count.Should().Be(PricesPerMarket * MarketCount);
-        results.Summary.Overall.Adds.Should().Be(PricesPerMarket * MarketCount);
-        results.Summary.Overall.Removes.Should().Be(0);
-        results.Summary.Overall.Updates.Should().Be(0);
-        results.Summary.Overall.Refreshes.Should().Be(0);
-    }
-
-    [Theory]
-    [InlineData(false, false)]
-    [InlineData(false, true)]
-    [InlineData(true, false)]
-    [InlineData(true, true)]
-    public void MergedObservableCompletesOnlyWhenSourceAndAllChildrenComplete(bool completeSource, bool completeChildren)
-    {
-        // having
-        _marketCache.AddOrUpdate(Enumerable.Range(0, MarketCount).Select(n => new FixedMarket(GetRandomPrice, n * ItemIdStride, (n * ItemIdStride) + PricesPerMarket, completable: completeChildren)));
-        var hasSourceSequenceCompleted = false;
-        var hasMergedSequenceCompleted = false;
-
-        using var cleanup = _marketCache.Connect().Do(_ => { }, () => hasSourceSequenceCompleted = true)
-                            .MergeManyChangeSets(m => m.LatestPrices, Market.RatingCompare).Subscribe(_ => { }, () => hasMergedSequenceCompleted = true);
-
-        // when
-        if (completeSource)
-        {
-            DisposeMarkets();
-        }
-
-        // then
-        hasSourceSequenceCompleted.Should().Be(completeSource);
-        hasMergedSequenceCompleted.Should().Be(completeSource && completeChildren);
-    }
-
-    [Fact]
-    public void MergedObservableWillFailIfSourceFails()
-    {
-        // having
-        var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
-        _marketCache.AddOrUpdate(markets);
-        var receivedError = default(Exception);
-        var expectedError = new Exception("Test exception");
-        var throwObservable = Observable.Throw<IChangeSet<IMarket, Guid>>(expectedError);
-
-        using var cleanup = _marketCache.Connect().Concat(throwObservable)
-                            .MergeManyChangeSets(m => m.LatestPrices, Market.RatingCompare).Subscribe(_ => { }, err => receivedError = err);
-
-        // when
-        DisposeMarkets();
-
-        // then
-        receivedError.Should().Be(expectedError);
-    }
-
-    private IObservable<IChangeSet<MarketPrice, int>> CreateChangeSet(string name, IComparer<IMarket>? sourceComp = null, IComparer<MarketPrice>? childCompare = null, IEqualityComparer<MarketPrice>? equalityComparer = null, bool resortOnRefresh = true) =>
-        _marketCache.Connect()
-            .DebugSpy(name)
-            .MergeManyChangeSets(m => m.LatestPrices.DebugSpy($"{name} [{m.Name} Prices]"), sourceComp ?? Market.RatingCompare, resortOnSourceRefresh: resortOnRefresh, equalityComparer, childCompare)
-            .DebugSpy($"{name} [Results]");
-
-    private IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRating(bool resortOnRefresh = true) => CreateChangeSet("Rating", resortOnRefresh: resortOnRefresh);
-    private IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRatingThenHighPrice(bool resortOnRefresh = true) => CreateChangeSet("Rating | High", Market.RatingCompare, MarketPrice.HighPriceCompare, resortOnRefresh: resortOnRefresh);
-    private IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRatingThenLowPrice(bool resortOnRefresh = true) => CreateChangeSet("Rating | Low", Market.RatingCompare, MarketPrice.LowPriceCompare, resortOnRefresh: resortOnRefresh);
-    private IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRatingThenRecent(bool resortOnRefresh = true) => CreateChangeSet("Rating | Recent", Market.RatingCompare, MarketPrice.LatestPriceCompare, equalityComparer: MarketPrice.EqualityComparer, resortOnRefresh: resortOnRefresh);
-    private IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRatingThenTimeStamp(bool resortOnRefresh = true) => CreateChangeSet("Rating | Timestamp", Market.RatingCompare, MarketPrice.LatestPriceCompare, equalityComparer: MarketPrice.EqualityComparerWithTimeStamp, resortOnRefresh: resortOnRefresh);
-    private IObservable<IChangeSet<MarketPrice, int>> ChangeSetByLowRating(bool resortOnRefresh = true) => CreateChangeSet("Low Rating", Market.RatingCompare.Invert(), resortOnRefresh: resortOnRefresh);
-    private IObservable<IChangeSet<MarketPrice, int>> ChangeSetByLowRatingThenHighPrice(bool resortOnRefresh = true) => CreateChangeSet("Low Rating | High", Market.RatingCompare.Invert(), MarketPrice.HighPriceCompare, resortOnRefresh: resortOnRefresh);
-    private IObservable<IChangeSet<MarketPrice, int>> ChangeSetByLowRatingThenLowPrice(bool resortOnRefresh = true) => CreateChangeSet("Low Rating | Low", Market.RatingCompare.Invert(), MarketPrice.LowPriceCompare, resortOnRefresh: resortOnRefresh);
-
-    private IMarket SetRating(IMarket market, double newRating)
-    {
-        market.Rating = newRating;
-        _marketCache.Refresh(market);
-        return market;
-    }
-
-    public void Dispose()
-    {
-        _marketCacheResults.Dispose();
-        DisposeMarkets();
-    }
-
-    private void CheckResultContents(ChangeSetAggregator<IMarket, Guid> marketResults, ChangeSetAggregator<MarketPrice, int> priceResults, IComparer<IMarket> comparer)
-    {
-        var expectedMarkets = _marketCache.Items.ToList();
-
-        // These should be subsets of each other
-        expectedMarkets.Should().BeSubsetOf(marketResults.Data.Items);
-        marketResults.Data.Items.Count.Should().Be(expectedMarkets.Count);
-
-        // Pair up all the Markets/Prices, Group them by ItemId, and sort each Group by the Market comparer
-        // Then pull out the first value from each group, which should be the price from the best market for each ItemId
-        var expectedPrices = expectedMarkets.Select(m => (Market)m).SelectMany(m => m.PricesCache.Items.Select(mp => (Market: m, MarketPrice: mp)))
-            .GroupBy(tuple => tuple.MarketPrice.ItemId)
-            .Select(group => group.OrderBy(tuple => tuple.Market, comparer).Select(tuple => tuple.MarketPrice).First())
-            .ToList();
-
-        // These should be subsets of each other
-        expectedPrices.Should().BeSubsetOf(priceResults.Data.Items);
-        priceResults.Data.Items.Count.Should().Be(expectedPrices.Count);
-    }
-
-    private void DisposeMarkets()
-    {
-        _marketCache.Items.ForEach(m => (m as IDisposable)?.Dispose());
-        _marketCache.Dispose();
-        _marketCache.Clear();
-    }
-
-    private decimal GetRandomPrice() => MarketPrice.RandomPrice(_randomizer, BasePrice, PriceOffset);
-}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithSourceComparer.IntegrationTests.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithSourceComparer.IntegrationTests.cs
new file mode 100644
index 000000000..73d513786
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithSourceComparer.IntegrationTests.cs
@@ -0,0 +1,137 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reactive;
+using System.Reactive.Concurrency;
+using System.Reactive.Disposables;
+using System.Reactive.Linq;
+using System.Reactive.Threading.Tasks;
+using System.Threading.Tasks;
+
+using Bogus;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Tests.Domain;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForCacheChangeSets
+    {
+        public static partial class WithSourceComparer
+        {
+            public sealed class IntegrationTests
+                : IntegrationTestFixtureBase
+            {
+                [Theory]
+                [InlineData(5, 7)]
+                [InlineData(10, 50)]
+                public async Task MultiThreadedStressTest(int marketCount, int priceCount)
+                {
+                    const int MaxItemId = 50;
+                    var MaxAddTime = TimeSpan.FromSeconds(0.250);
+                    var MaxRemoveTime = TimeSpan.FromSeconds(0.100);
+
+                    var randomizer = new Randomizer(0x10012022);
+                    var marketFaker = Fakers.Market.RuleFor(m => m.Rating, faker => faker.Random.Double(0, 5)).WithSeed(randomizer);
+                    
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var merged = marketCache.Connect().MergeManyChangeSets(market => market.LatestPrices, Market.RatingCompare, resortOnSourceRefresh: true).Publish();
+                    var adding = true;
+                    var cacheCompleted = merged.LastOrDefaultAsync().ToTask();
+                    using var priceResults = merged.AsAggregator();
+                    using var connect = merged.Connect();
+
+                    // Start asynchrononously modifying the parent list and the child lists
+                    using var addingSub = AddRemoveStress(marketCount, priceCount, Environment.ProcessorCount, TaskPoolScheduler.Default)
+                        .Finally(() => adding = false)
+                        .Subscribe();
+
+                    // Subscribe / unsubscribe over and over while the collections are being modified
+                    do
+                    {
+                        // Ensure items are being added asynchronously before subscribing to changes
+                        await Task.Yield();
+
+                        {
+                            // Subscribe
+                            var mergedSub = merged.Subscribe();
+
+                            // Let other threads run
+                            await Task.Yield();
+
+                            // Unsubscribe
+                            mergedSub.Dispose();
+                        }
+                    }
+                    while (adding);
+
+                    // Wait for the source cache to finish delivering all notifications.
+                    await cacheCompleted;
+
+                    // Verify the results
+                    CheckResultContents(marketCache, marketCacheResults, priceResults, Market.RatingCompare);
+
+
+                    TimeSpan? GetRemoveTime() => randomizer.Bool() ? randomizer.TimeSpan(MaxRemoveTime) : null;
+
+                    IObservable<Unit> AddRemoveStress(int marketCount, int priceCount, int parallel, IScheduler scheduler) =>
+                        Observable.Create<Unit>(observer => new CompositeDisposable
+                        {
+                            AddRemoveMarkets(marketCount, parallel, scheduler)
+                                .Subscribe(
+                                    onNext: static _ => { },
+                                    onError: observer.OnError),
+                            marketCache.Connect()
+                                .MergeMany(market => AddRemovePrices((Market)market, priceCount, parallel, scheduler))
+                                .Subscribe(
+                                    onNext: static _ => { },
+                                    onError: observer.OnError,
+                                    onCompleted: observer.OnCompleted)
+                        });
+
+                    IObservable<IMarket> AddRemoveMarkets(int ownerCount, int parallel, IScheduler scheduler) =>
+                        marketFaker.IntervalGenerate(MaxAddTime, scheduler)
+                            .Parallelize(ownerCount, parallel, obs => obs.StressAddRemove(marketCache, _ => GetRemoveTime(), scheduler))
+                            .Finally(marketCache.Dispose);
+
+                    IObservable<MarketPrice> AddRemovePrices(Market market, int priceCount, int parallel, IScheduler scheduler) =>
+                        randomizer.Interval(MaxAddTime, scheduler).Select(_ => market.CreatePrice(randomizer.Number(MaxItemId), GetRandomPrice(randomizer)))
+                            .Parallelize(priceCount, parallel, obs => obs.StressAddRemove(market.PricesCache, _ => GetRemoveTime(), scheduler))
+                            .Finally(market.PricesCache.Dispose);
+                }
+
+                private static void CheckResultContents(
+                    SourceCache<IMarket, Guid> marketCache,
+                    ChangeSetAggregator<IMarket, Guid> marketResults,
+                    ChangeSetAggregator<MarketPrice, int> priceResults,
+                    IComparer<IMarket> comparer)
+                {
+                    var expectedMarkets = marketCache.Items.ToList();
+
+                    // These should be subsets of each other
+                    expectedMarkets.Should().BeSubsetOf(marketResults.Data.Items);
+                    marketResults.Data.Items.Count.Should().Be(expectedMarkets.Count);
+
+                    // Pair up all the Markets/Prices, Group them by ItemId, and sort each Group by the Market comparer
+                    // Then pull out the first value from each group, which should be the price from the best market for each ItemId
+                    var expectedPrices = expectedMarkets.Select(m => (Market)m).SelectMany(m => m.PricesCache.Items.Select(mp => (Market: m, MarketPrice: mp)))
+                        .GroupBy(tuple => tuple.MarketPrice.ItemId)
+                        .Select(group => group.OrderBy(tuple => tuple.Market, comparer).Select(tuple => tuple.MarketPrice).First())
+                        .ToList();
+
+                    // These should be subsets of each other
+                    expectedPrices.Should().BeSubsetOf(priceResults.Data.Items);
+                    priceResults.Data.Items.Count.Should().Be(expectedPrices.Count);
+                }
+            }
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithSourceComparer.UnitTests.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithSourceComparer.UnitTests.cs
new file mode 100644
index 000000000..641cdd499
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithSourceComparer.UnitTests.cs
@@ -0,0 +1,1192 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reactive.Linq;
+
+using Bogus;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Kernel;
+using DynamicData.Tests.Domain;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForCacheChangeSets
+    {
+        public static partial class WithSourceComparer
+        {
+            public class UnitTests
+            {
+                [Fact]
+                public void AbleToInvokeFactory()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    // having
+                    var invoked = false;
+                    IObservable<IChangeSet<MarketPrice, int>> factory(IMarket m)
+                    {
+                        invoked = true;
+                        return m.LatestPrices;
+                    }
+                    using var sub = marketCache.Connect().MergeManyChangeSets(factory, Market.RatingCompare).Subscribe();
+
+                    // when
+                    marketCache.AddOrUpdate(new Market(0));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    invoked.Should().BeTrue();
+                }
+
+                [Fact]
+                public void AbleToInvokeFactoryWithKey()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    // having
+                    var invoked = false;
+                    IObservable<IChangeSet<MarketPrice, int>> factory(IMarket m, Guid g)
+                    {
+                        invoked = true;
+                        return m.LatestPrices;
+                    }
+                    using var sub = marketCache.Connect().MergeManyChangeSets(factory, Market.RatingCompare).Subscribe();
+
+                    // when
+                    marketCache.AddOrUpdate(new Market(0));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    invoked.Should().BeTrue();
+                }
+
+                [Fact]
+                public void AllExistingSubItemsPresentInResult()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, () => GetRandomPrice(randomizer)));
+
+                    // when
+                    marketCache.AddOrUpdate(markets);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount);
+                    markets.Sum(m => m.PricesCache.Count).Should().Be(MarketCount * PricesPerMarket);
+                    results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
+                    results.Messages.Count.Should().Be(1);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void AllNewSubItemsPresentInResult()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+
+                    // when
+                    markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, () => GetRandomPrice(randomizer)));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount);
+                    markets.Sum(m => m.PricesCache.Count).Should().Be(MarketCount * PricesPerMarket);
+                    results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
+                    results.Messages.Count.Should().Be(MarketCount);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void AllRefreshedSubItemsAreRefreshed()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, () => GetRandomPrice(randomizer)));
+                    marketCache.AddOrUpdate(markets);
+
+                    // when
+                    markets.ForEach(m => m.RefreshAllPrices(() => GetRandomPrice(randomizer)));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount);
+                    results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
+                    results.Messages.Count.Should().Be(MarketCount + 1);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(MarketCount * PricesPerMarket);
+                }
+
+                [Fact]
+                public void AnyDuplicateKeyValuesShouldBeHidden()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    markets[0].Rating = 1.0;
+                    marketCache.AddOrUpdate(markets);
+
+                    // when
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void AnyDuplicateValuesShouldBeNoOpWhenRemoved()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    markets[0].Rating = 1.0;
+                    marketCache.AddOrUpdate(markets);
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // when
+                    markets[1].RemoveAllPrices();
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void AnyDuplicateValuesShouldBeUnhiddenWhenOtherIsRemoved()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    markets[0].Rating = 1.0;
+                    marketCache.AddOrUpdate(markets);
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // when
+                    marketCache.Remove(markets[0]);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Data.Items.Zip(markets[1].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                    results.Messages.Count.Should().Be(2);
+                    results.Messages[1].Updates.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void AnyDuplicateValuesShouldNotRefreshWhenHidden()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    markets[0].Rating = 1.0;
+                    marketCache.AddOrUpdate(markets);
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // when
+                    markets[1].RefreshAllPrices(() => GetRandomPrice(randomizer));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void AnyRemovedSubItemIsRemoved()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+                    markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, () => GetRandomPrice(randomizer)));
+
+                    // when
+                    markets.ForEach(m => m.PricesCache.Edit(updater => updater.RemoveKeys(updater.Keys.Take(RemoveCount))));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount);
+                    results.Data.Count.Should().Be(MarketCount * (PricesPerMarket - RemoveCount));
+                    results.Messages.Count.Should().Be(MarketCount * 2);
+                    results.Messages[0].Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(MarketCount * RemoveCount);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void AnySourceItemRemovedRemovesAllSourceValues()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+                    markets.Select((m, index) => new { Market = m, Index = index }).ForEach(m => m.Market.SetPrices(m.Index * ItemIdStride, (m.Index * ItemIdStride) + PricesPerMarket, () => GetRandomPrice(randomizer)));
+
+                    // when
+                    marketCache.Edit(updater => updater.RemoveKeys(updater.Keys.Take(RemoveCount)));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount - RemoveCount);
+                    results.Data.Count.Should().Be((MarketCount - RemoveCount) * PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(PricesPerMarket * RemoveCount);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void BestChoiceFromDuplicatesSelectedWhenChangeSetCreated()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var marketOriginal = new Market(0);
+                    var marketBetter = new Market(1);
+                    marketBetter.Rating = 1.0;
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketBetter.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketBetter);
+
+                    // when
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+                    using var resultsLow = ChangeSetByLowRating(marketCache, false).AsAggregator();
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
+                    resultsLow.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Updates.Should().Be(0);
+                    resultsLow.Summary.Overall.Removes.Should().Be(0);
+                    resultsLow.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                }
+
+                [Fact]
+                public void ChangingSourceByUpdateRemovesPreviousAndAddsNewValues()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+                    var market = new Market(0);
+                    market.SetPrices(0, PricesPerMarket * 2, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(market);
+                    var updatedMarket = new Market(market);
+                    updatedMarket.SetPrices(PricesPerMarket, PricesPerMarket * 3, () => GetRandomPrice(randomizer));
+
+                    // when
+                    marketCache.AddOrUpdate(updatedMarket);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    results.Data.Count.Should().Be(PricesPerMarket * 2);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket * 3);
+                    results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Zip(updatedMarket.PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                }
+
+                [Fact]
+                public void ChangingSourceByUpdateRemovesPreviousAndEmitsBetterValues()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+                    var market = new Market(0);
+                    var marketWorse = new Market(1);
+                    SetRating(marketCache, marketWorse, -1);
+                    market.SetPrices(0, PricesPerMarket * 2, () => GetRandomPrice(randomizer));
+                    marketWorse.SetPrices(0, PricesPerMarket * 2, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(market);
+                    marketCache.AddOrUpdate(marketWorse);
+
+                    var updatedMarket = new Market(market);
+                    updatedMarket.SetPrices(PricesPerMarket, PricesPerMarket * 3, () => GetRandomPrice(randomizer));
+
+                    // when
+                    marketCache.AddOrUpdate(updatedMarket);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket * 3);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket * 3);
+                    results.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Take(PricesPerMarket).Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketWorse.Id));
+                    results.Data.Items.Skip(PricesPerMarket).Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(updatedMarket.Id));
+                }
+
+                [Fact]
+                public void ChildComparerOnlyRefreshesVisibleValues()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+                    using var lowRatingLowPriceResults = ChangeSetByLowRatingThenLowPrice(marketCache, false).AsAggregator();
+                    using var lowRatingHighPriceResults = ChangeSetByLowRatingThenHighPrice(marketCache, false).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketLow = new Market(1);
+                    var marketLowest = new Market(2);
+
+                    marketLowest.Rating = marketLow.Rating = -1;
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketLow.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketLowest.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketLow);
+                    marketCache.AddOrUpdate(marketLowest);
+
+                    // when
+                    marketLowest.RefreshAllPrices(LowestPrice - 1);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(3);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                    lowRatingLowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowRatingLowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowRatingLowPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowRatingLowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    lowRatingLowPriceResults.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
+                    lowRatingLowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLowest.Id));
+                    lowRatingHighPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowRatingHighPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowRatingHighPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowRatingHighPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    lowRatingHighPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    lowRatingHighPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
+                }
+
+                [Fact]
+                public void ChildComparerOnlyUpdatesVisibleValuesOnUpdate()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+                    using var lowRatingLowPriceResults = ChangeSetByLowRatingThenLowPrice(marketCache, false).AsAggregator();
+                    using var lowRatingHighPriceResults = ChangeSetByLowRatingThenHighPrice(marketCache, false).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketLow = new Market(1);
+                    var marketLowest = new Market(2);
+
+                    marketLowest.Rating = marketLow.Rating = -1;
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketLowest.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketLow);
+                    marketCache.AddOrUpdate(marketLowest);
+
+                    // when
+                    marketLowest.UpdateAllPrices(LowestPrice - 1);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(3);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                    lowRatingLowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowRatingLowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowRatingLowPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowRatingLowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    lowRatingLowPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    lowRatingLowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLowest.Id));
+                    lowRatingHighPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowRatingHighPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowRatingHighPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowRatingHighPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
+                    lowRatingHighPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    lowRatingHighPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
+                }
+
+                [Fact]
+                public void ChildComparerUpdatesToCorrectValueOnUpdate()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var resultsLow = ChangeSetByLowRating(marketCache, false).AsAggregator();
+                    using var resultsLowPrice = ChangeSetByRatingThenLowPrice(marketCache, false).AsAggregator();
+                    using var resultsHighPrice = ChangeSetByRatingThenHighPrice(marketCache, false).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketHighest = new Market(1);
+                    var marketLowest = new Market(2);
+                    marketLowest.Rating = marketHighest.Rating = 1.0;
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketHighest.SetPrices(0, PricesPerMarket, HighestPrice);
+                    marketLowest.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketHighest);
+                    marketCache.AddOrUpdate(marketLowest);
+
+                    // when
+                    marketLowest.UpdateAllPrices(LowestPrice);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(3);
+                    resultsLow.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Updates.Should().Be(0);
+                    resultsLow.Summary.Overall.Removes.Should().Be(0);
+                    resultsLow.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+
+                    resultsLowPrice.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLowPrice.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLowPrice.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
+                    resultsLowPrice.Summary.Overall.Removes.Should().Be(0);
+                    resultsLowPrice.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsLowPrice.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLowest.Id));
+
+                    resultsHighPrice.Data.Count.Should().Be(PricesPerMarket);
+                    resultsHighPrice.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsHighPrice.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    resultsHighPrice.Summary.Overall.Removes.Should().Be(0);
+                    resultsHighPrice.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsHighPrice.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketHighest.Id));
+                }
+
+                [Fact]
+                public void EqualityComparerAndChildComparerRefreshesBecomeUpdates()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var resultsLow = ChangeSetByLowRating(marketCache).AsAggregator();
+                    using var resultsRecent = ChangeSetByRatingThenRecent(marketCache).AsAggregator();
+                    using var resultsTimeStamp = ChangeSetByRatingThenTimeStamp(marketCache).AsAggregator();
+                    var marketLow = new Market(0);
+                    var market = new Market(1);
+                    marketLow.Rating = -1;
+                    marketLow.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    market.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketLow);
+                    marketCache.AddOrUpdate(market);
+                    market.SetPrices(0, PricesPerMarket, LowestPrice);
+                    // Update again, but only the timestamp will change, so resultsRecent will ignore
+                    market.SetPrices(0, PricesPerMarket, LowestPrice);
+
+                    // when
+                    // resultsRecent won't see the refresh because it ignored the update
+                    // resultsTimeStamp will see the refreshes because it didn't
+                    market.RefreshAllPrices(() => GetRandomPrice(randomizer));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    resultsLow.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLow.Messages.Count.Should().Be(1);
+                    resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Removes.Should().Be(0);
+                    resultsLow.Summary.Overall.Updates.Should().Be(0);
+                    resultsLow.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsRecent.Messages.Count.Should().Be(4);
+                    resultsRecent.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsRecent.Summary.Overall.Removes.Should().Be(0);
+                    resultsRecent.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
+                    resultsRecent.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsTimeStamp.Messages.Count.Should().Be(5);
+                    resultsTimeStamp.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsTimeStamp.Summary.Overall.Removes.Should().Be(0);
+                    resultsTimeStamp.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
+                    resultsTimeStamp.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
+                }
+
+                [Fact]
+                public void EqualityComparerAndChildComparerWorkTogetherForRefreshes()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var resultsLow = ChangeSetByLowRating(marketCache).AsAggregator();
+                    using var resultsRecent = ChangeSetByRatingThenRecent(marketCache).AsAggregator();
+                    using var resultsTimeStamp = ChangeSetByRatingThenTimeStamp(marketCache).AsAggregator();
+                    var marketLow = new Market(0);
+                    var market = new Market(1);
+                    marketLow.Rating = -1;
+                    marketLow.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    market.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketLow);
+                    marketCache.AddOrUpdate(market);
+                    market.SetPrices(0, PricesPerMarket, LowestPrice);
+                    // Update again, but only the timestamp will change, so resultsRecent will ignore
+                    market.SetPrices(0, PricesPerMarket, LowestPrice);
+
+                    // when
+                    // resultsRecent won't see the refresh because it ignored the update
+                    // resultsTimeStamp will see the refreshes because it didn't
+                    market.RefreshAllPrices(LowestPrice);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    resultsLow.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLow.Messages.Count.Should().Be(1);
+                    resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Removes.Should().Be(0);
+                    resultsLow.Summary.Overall.Updates.Should().Be(0);
+                    resultsLow.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsRecent.Messages.Count.Should().Be(4);
+                    resultsRecent.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsRecent.Summary.Overall.Removes.Should().Be(0);
+                    resultsRecent.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    resultsRecent.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
+                    resultsTimeStamp.Messages.Count.Should().Be(5);
+                    resultsTimeStamp.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsTimeStamp.Summary.Overall.Removes.Should().Be(0);
+                    resultsTimeStamp.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
+                    resultsTimeStamp.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
+                }
+
+                [Fact]
+                public void EqualityComparerAndChildComparerWorkTogetherForUpdates()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var resultsLow = ChangeSetByLowRating(marketCache).AsAggregator();
+                    using var resultsRecent = ChangeSetByRatingThenRecent(marketCache).AsAggregator();
+                    using var resultsTimeStamp = ChangeSetByRatingThenTimeStamp(marketCache).AsAggregator();
+                    var marketLow = new Market(0);
+                    var market = new Market(1);
+                    marketLow.Rating = -1;
+                    marketLow.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    market.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketLow);
+                    marketCache.AddOrUpdate(market);
+                    market.SetPrices(0, PricesPerMarket, LowestPrice);
+
+                    // when
+                    market.UpdateAllPrices(LowestPrice);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    resultsLow.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLow.Messages.Count.Should().Be(1);
+                    resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Removes.Should().Be(0);
+                    resultsLow.Summary.Overall.Updates.Should().Be(0);
+                    resultsLow.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsRecent.Messages.Count.Should().Be(3);
+                    resultsRecent.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsRecent.Summary.Overall.Removes.Should().Be(0);
+                    resultsRecent.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    resultsRecent.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsTimeStamp.Messages.Count.Should().Be(4);
+                    resultsTimeStamp.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsTimeStamp.Summary.Overall.Removes.Should().Be(0);
+                    resultsTimeStamp.Summary.Overall.Updates.Should().Be(PricesPerMarket * 3);
+                    resultsTimeStamp.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void EqualityComparerHidesUpdatesWithoutChanges()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    // having
+                    var market = new Market(0);
+                    using var results = CreateChangeSet(marketCache, "Equality Compare", Market.RatingCompare, equalityComparer: MarketPrice.EqualityComparer, resortOnRefresh: true).AsAggregator();
+                    market.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketCache.AddOrUpdate(market);
+
+                    // when
+                    market.SetPrices(0, PricesPerMarket, LowestPrice);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Messages.Count.Should().Be(1);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void EveryItemVisibleWhenSequenceCompletes()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    marketCache.AddOrUpdate(Enumerable.Range(0, MarketCount).Select(n => new FixedMarket(() => GetRandomPrice(randomizer), n * ItemIdStride, (n * ItemIdStride) + PricesPerMarket)));
+
+                    // when
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+                    marketCache.Items.ForEach(m => (m as IDisposable)?.Dispose());
+                    marketCache.Dispose();
+
+                    // then
+                    results.Data.Count.Should().Be(PricesPerMarket * MarketCount);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket * MarketCount);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Theory]
+                [InlineData(false, false)]
+                [InlineData(false, true)]
+                [InlineData(true, false)]
+                [InlineData(true, true)]
+                public void MergedObservableCompletesOnlyWhenSourceAndAllChildrenComplete(bool completeSource, bool completeChildren)
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    marketCache.AddOrUpdate(Enumerable.Range(0, MarketCount).Select(n => new FixedMarket(() => GetRandomPrice(randomizer), n * ItemIdStride, (n * ItemIdStride) + PricesPerMarket, completable: completeChildren)));
+                    var hasSourceSequenceCompleted = false;
+                    var hasMergedSequenceCompleted = false;
+
+                    using var cleanup = marketCache.Connect().Do(_ => { }, () => hasSourceSequenceCompleted = true)
+                        .MergeManyChangeSets(m => m.LatestPrices, Market.RatingCompare).Subscribe(_ => { }, () => hasMergedSequenceCompleted = true);
+
+                    // when
+                    if (completeSource)
+                    {
+                        marketCache.Items.ForEach(m => (m as IDisposable)?.Dispose());
+                        marketCache.Dispose();
+                    }
+
+                    // then
+                    hasSourceSequenceCompleted.Should().Be(completeSource);
+                    hasMergedSequenceCompleted.Should().Be(completeSource && completeChildren);
+                }
+
+                [Fact]
+                public void MergedObservableWillFailIfSourceFails()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    marketCache.AddOrUpdate(markets);
+                    var receivedError = default(Exception);
+                    var expectedError = new Exception("Test exception");
+                    var throwObservable = Observable.Throw<IChangeSet<IMarket, Guid>>(expectedError);
+
+                    using var cleanup = marketCache.Connect().Concat(throwObservable)
+                        .MergeManyChangeSets(m => m.LatestPrices, Market.RatingCompare).Subscribe(_ => { }, err => receivedError = err);
+
+                    // when
+                    marketCache.Items.ForEach(m => (m as IDisposable)?.Dispose());
+                    marketCache.Dispose();
+
+                    // then
+                    receivedError.Should().Be(expectedError);
+                }
+
+                [Fact]
+                public void NullChecks()
+                {
+                    // having
+                    var emptyChangeSetObs = Observable.Empty<IChangeSet<int, int>>();
+                    var nullChangeSetObs = (IObservable<IChangeSet<int, int>>)null!;
+                    var emptyChildChangeSetObs = Observable.Empty<IChangeSet<string, string>>();
+                    var emptySelector = new Func<int, IObservable<IChangeSet<string, string>>>(i => emptyChildChangeSetObs);
+                    var emptyKeySelector = new Func<int, int, IObservable<IChangeSet<string, string>>>((i, key) => emptyChildChangeSetObs);
+                    var nullSelector = (Func<int, IObservable<IChangeSet<string, string>>>)null!;
+                    var nullKeySelector = (Func<int, int, IObservable<IChangeSet<string, string>>>)null!;
+                    var nullParentComparer = (IComparer<int>)null!;
+                    var emptyParentComparer = new NoOpComparer<int>() as IComparer<int>;
+                    var nullChildComparer = (IComparer<string>)null!;
+                    var emptyChildComparer = new NoOpComparer<string>() as IComparer<string>;
+                    var nullEqualityComparer = (IEqualityComparer<string>)null!;
+                    var emptyEqualityComparer = new NoOpEqualityComparer<string>() as IEqualityComparer<string>;
+
+                    // when
+                    var actionParentCompare1 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector, sourceComparer: emptyParentComparer);
+                    var actionParentCompareKey1a = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector, sourceComparer: emptyParentComparer);
+                    var actionParentCompareKey1b = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector, sourceComparer: emptyParentComparer);
+                    var actionParentCompareKey1c = () => emptyChangeSetObs.MergeManyChangeSets(emptyKeySelector, sourceComparer: nullParentComparer);
+                    var actionParentCompare2 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector, sourceComparer: emptyParentComparer, equalityComparer: emptyEqualityComparer);
+                    var actionParentCompareKey2a = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector, sourceComparer: emptyParentComparer, equalityComparer: emptyEqualityComparer);
+                    var actionParentCompareKey2b = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector, sourceComparer: emptyParentComparer, equalityComparer: emptyEqualityComparer);
+
+                    // then
+                    emptyChangeSetObs.Should().NotBeNull();
+                    emptyChildChangeSetObs.Should().NotBeNull();
+                    emptyChildComparer.Should().NotBeNull();
+                    emptyEqualityComparer.Should().NotBeNull();
+                    emptyKeySelector.Should().NotBeNull();
+                    emptyParentComparer.Should().NotBeNull();
+                    emptySelector.Should().NotBeNull();
+                    nullChangeSetObs.Should().BeNull();
+                    nullChildComparer.Should().BeNull();
+                    nullEqualityComparer.Should().BeNull();
+                    nullKeySelector.Should().BeNull();
+                    nullParentComparer.Should().BeNull();
+                    nullSelector.Should().BeNull();
+
+                    actionParentCompare1.Should().Throw<ArgumentNullException>();
+                    actionParentCompareKey1a.Should().Throw<ArgumentNullException>();
+                    actionParentCompareKey1b.Should().Throw<ArgumentNullException>();
+                    actionParentCompareKey1c.Should().Throw<ArgumentNullException>();
+                    actionParentCompare2.Should().Throw<ArgumentNullException>();
+                    actionParentCompareKey2a.Should().Throw<ArgumentNullException>();
+                    actionParentCompareKey2b.Should().Throw<ArgumentNullException>();
+                }
+
+                [Fact]
+                public void OnlyAddsBetterValuesOnSourceUpdate()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+                    using var resultsLow = ChangeSetByLowRating(marketCache, false).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketBetter = new Market(1);
+                    marketBetter.Rating = 1.0;
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketBetter);
+
+                    // when
+                    marketBetter.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
+                    resultsLow.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Updates.Should().Be(0);
+                    resultsLow.Summary.Overall.Removes.Should().Be(0);
+                    resultsLow.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                }
+
+                [Fact]
+                public void OnlyUpdatesOnDuplicateIfNewItemIsFromBetterParent()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+                    using var resultsLow = ChangeSetByLowRating(marketCache, false).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketBetter = new Market(1);
+                    marketBetter.Rating = 1.0;
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketBetter.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+
+                    // when
+                    marketCache.AddOrUpdate(marketBetter);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
+                    resultsLow.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Updates.Should().Be(0);
+                    resultsLow.Summary.Overall.Removes.Should().Be(0);
+                    resultsLow.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                }
+
+                [Fact]
+                public void SourceRefreshDoesNothingIfDisabled()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache, resortOnRefresh: false).AsAggregator();
+                    markets[0].Rating = 1.0;
+                    marketCache.AddOrUpdate(markets);
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // when
+                    SetRating(marketCache, markets[1], 2.0);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void SourceRefreshGeneratesUpdatesAsNeeded()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = ChangeSetByRating(marketCache).AsAggregator();
+                    markets[0].Rating = 1.0;
+                    marketCache.AddOrUpdate(markets);
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // when
+                    SetRating(marketCache, markets[1], 2.0);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Data.Items.Zip(markets[1].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void UpdatesToCorrectValueOnRefresh()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+                    using var resultsLow = ChangeSetByLowRating(marketCache, false).AsAggregator();
+                    using var resultsRefresh = ChangeSetByRating(marketCache, true).AsAggregator();
+                    using var resultsLowRefresh = ChangeSetByLowRating(marketCache, true).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketBetter = new Market(1);
+                    marketBetter.Rating = -1.0;
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketBetter.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketBetter);
+
+                    // when
+                    SetRating(marketCache, marketBetter, 2.0);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    marketCacheResults.Summary.Overall.Refreshes.Should().Be(1);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                    resultsLow.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    resultsLow.Summary.Overall.Removes.Should().Be(0);
+                    resultsLow.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsLow.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
+                    resultsRefresh.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsRefresh.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    resultsRefresh.Summary.Overall.Removes.Should().Be(0);
+                    resultsRefresh.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsRefresh.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
+                    resultsLowRefresh.Data.Count.Should().Be(PricesPerMarket);
+                    resultsLowRefresh.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    resultsLowRefresh.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    resultsLowRefresh.Summary.Overall.Removes.Should().Be(0);
+                    resultsLowRefresh.Summary.Overall.Refreshes.Should().Be(0);
+                    resultsLowRefresh.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                }
+                [Fact]
+                public void UpdatesToCorrectValueOnRemove()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x10012022);
+
+                    // having
+                    var marketOriginal = new Market(0);
+                    var marketBetter = new Market(1);
+                    var marketBest = new Market(2);
+                    marketBetter.Rating = 1.0;
+                    marketBest.Rating = 5.0;
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketBetter.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketBest.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketBest);
+                    marketCache.AddOrUpdate(marketBetter);
+                    using var results = ChangeSetByRating(marketCache, false).AsAggregator();
+
+                    // when
+                    marketCache.Remove(marketBest);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketBetter.Id));
+                }
+
+                private static IObservable<IChangeSet<MarketPrice, int>> CreateChangeSet(
+                        SourceCache<IMarket, Guid> marketCache,
+                        string name,
+                        IComparer<IMarket>? sourceComp = null,
+                        IComparer<MarketPrice>? childCompare = null,
+                        IEqualityComparer<MarketPrice>? equalityComparer = null,
+                        bool resortOnRefresh = true) =>
+                    marketCache.Connect()
+                        .DebugSpy(name)
+                        .MergeManyChangeSets(m => m.LatestPrices.DebugSpy($"{name} [{m.Name} Prices]"), sourceComp ?? Market.RatingCompare, resortOnSourceRefresh: resortOnRefresh, equalityComparer, childCompare)
+                        .DebugSpy($"{name} [Results]");
+
+                private static IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRating(
+                        SourceCache<IMarket, Guid> marketCache,
+                        bool resortOnRefresh = true)
+                    => CreateChangeSet(
+                        marketCache: marketCache,
+                        name: "Rating",
+                        resortOnRefresh: resortOnRefresh);
+                
+                private static IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRatingThenHighPrice(
+                        SourceCache<IMarket, Guid> marketCache,
+                        bool resortOnRefresh = true)
+                    => CreateChangeSet(
+                        marketCache: marketCache,
+                        name: "Rating | High",
+                        sourceComp: Market.RatingCompare,
+                        childCompare: MarketPrice.HighPriceCompare,
+                        resortOnRefresh: resortOnRefresh);
+
+                private static IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRatingThenLowPrice(
+                        SourceCache<IMarket, Guid> marketCache,
+                        bool resortOnRefresh = true)
+                    => CreateChangeSet(
+                        marketCache: marketCache,
+                        name: "Rating | Low",
+                        sourceComp: Market.RatingCompare,
+                        childCompare: MarketPrice.LowPriceCompare,
+                        resortOnRefresh: resortOnRefresh);
+
+                private static IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRatingThenRecent(
+                        SourceCache<IMarket, Guid> marketCache,
+                        bool resortOnRefresh = true)
+                    => CreateChangeSet(
+                        marketCache: marketCache,
+                        name: "Rating | Recent",
+                        sourceComp: Market.RatingCompare,
+                        childCompare: MarketPrice.LatestPriceCompare,
+                        equalityComparer: MarketPrice.EqualityComparer,
+                        resortOnRefresh: resortOnRefresh);
+                
+                private static IObservable<IChangeSet<MarketPrice, int>> ChangeSetByRatingThenTimeStamp(
+                        SourceCache<IMarket, Guid> marketCache,
+                        bool resortOnRefresh = true)
+                    => CreateChangeSet(
+                        marketCache: marketCache,
+                        name: "Rating | Timestamp",
+                        sourceComp: Market.RatingCompare,
+                        childCompare: MarketPrice.LatestPriceCompare,
+                        equalityComparer: MarketPrice.EqualityComparerWithTimeStamp,
+                        resortOnRefresh: resortOnRefresh);
+
+                private static IObservable<IChangeSet<MarketPrice, int>> ChangeSetByLowRating(
+                        SourceCache<IMarket, Guid> marketCache,
+                        bool resortOnRefresh = true)
+                    => CreateChangeSet(
+                        marketCache: marketCache,
+                        name: "Low Rating",
+                        sourceComp: Market.RatingCompare.Invert(),
+                        resortOnRefresh: resortOnRefresh);
+                
+                private static IObservable<IChangeSet<MarketPrice, int>> ChangeSetByLowRatingThenHighPrice(
+                        SourceCache<IMarket, Guid> marketCache,
+                        bool resortOnRefresh = true)
+                    => CreateChangeSet(
+                        marketCache: marketCache,
+                        name: "Low Rating | High",
+                        sourceComp: Market.RatingCompare.Invert(),
+                        childCompare: MarketPrice.HighPriceCompare,
+                        resortOnRefresh: resortOnRefresh);
+                
+                private static IObservable<IChangeSet<MarketPrice, int>> ChangeSetByLowRatingThenLowPrice(
+                        SourceCache<IMarket, Guid> marketCache,
+                        bool resortOnRefresh = true)
+                    => CreateChangeSet(
+                        marketCache: marketCache,
+                        name: "Low Rating | Low",
+                        sourceComp: Market.RatingCompare.Invert(),
+                        childCompare: MarketPrice.LowPriceCompare,
+                        resortOnRefresh: resortOnRefresh);
+
+                private static IMarket SetRating(
+                    SourceCache<IMarket, Guid> marketCache,
+                    IMarket market,
+                    double newRating)
+                {
+                    market.Rating = newRating;
+                    marketCache.Refresh(market);
+                    return market;
+                }
+
+            }
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithSourceComparer.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithSourceComparer.cs
new file mode 100644
index 000000000..fa9b0bbd5
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithSourceComparer.cs
@@ -0,0 +1,9 @@
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForCacheChangeSets
+    {
+        public static partial class WithSourceComparer;
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithoutSourceComparer.IntegrationTests.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithoutSourceComparer.IntegrationTests.cs
new file mode 100644
index 000000000..b13e201eb
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithoutSourceComparer.IntegrationTests.cs
@@ -0,0 +1,134 @@
+using System;
+using System.Linq;
+using System.Reactive;
+using System.Reactive.Concurrency;
+using System.Reactive.Disposables;
+using System.Reactive.Linq;
+using System.Reactive.Threading.Tasks;
+using System.Threading.Tasks;
+
+using Bogus;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Tests.Domain;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForCacheChangeSets
+    {
+        public static partial class WithoutSourceComparer
+        {
+            public sealed class IntegrationTests
+                : IntegrationTestFixtureBase
+            {
+                [Theory]
+                [InlineData(5, 7)]
+                [InlineData(10, 50)]
+                #if !DEBUG
+                [InlineData(10, 1_000)]
+                [InlineData(200, 500)]
+                [InlineData(1_000, 10)]
+                #endif
+                public async Task MultiThreadedStressTest(int marketCount, int priceCount)
+                {
+                    var MaxAddTime = TimeSpan.FromSeconds(0.250);
+                    var MaxRemoveTime = TimeSpan.FromSeconds(0.100);
+
+                    var randomizer = new Randomizer(0x21123737);
+                    var marketFaker = Fakers.Market.WithSeed(randomizer);
+                    
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var merged = marketCache.Connect().MergeManyChangeSets(market => market.LatestPrices).Publish();
+                    var adding = true;
+                    var cacheCompleted = merged.LastOrDefaultAsync().ToTask();
+                    using var priceResults = merged.AsAggregator();
+                    using var connect = merged.Connect();
+
+                    // Start asynchrononously modifying the parent list and the child lists
+                    using var addingSub = AddRemoveStress(marketCount, priceCount, Environment.ProcessorCount, TaskPoolScheduler.Default)
+                        .Finally(() => adding = false)
+                        .Subscribe();
+
+                    // Subscribe / unsubscribe over and over while the collections are being modified
+                    do
+                    {
+                        // Ensure items are being added asynchronously before subscribing to changes
+                        await Task.Yield();
+
+                        {
+                            // Subscribe
+                            var mergedSub = merged.Subscribe();
+
+                            // Let other threads run
+                            await Task.Yield();
+
+                            // Unsubscribe
+                            mergedSub.Dispose();
+                        }
+                    }
+                    while (adding);
+
+                    // Wait for the source cache to finish delivering all notifications.
+                    await cacheCompleted;
+
+                    // Verify the results
+                    CheckResultContents(marketCache, marketCacheResults, priceResults);
+
+
+                    TimeSpan? GetRemoveTime() => randomizer.Bool() ? randomizer.TimeSpan(MaxRemoveTime) : null;
+
+                    IObservable<Unit> AddRemoveStress(int marketCount, int priceCount, int parallel, IScheduler scheduler) =>
+                        Observable.Create<Unit>(observer => new CompositeDisposable
+                            (
+                                AddRemoveMarkets(marketCount, parallel, scheduler)
+                                    .Subscribe(
+                                        onNext: static _ => { },
+                                        onError: observer.OnError),
+
+                                marketCache.Connect()
+                                    .MergeMany(market => AddRemovePrices((Market)market, priceCount, parallel, scheduler))
+                                    .Subscribe(
+                                        onNext: static _ => { },
+                                        onError: observer.OnError,
+                                        onCompleted: observer.OnCompleted)
+                            ));
+
+                    IObservable<IMarket> AddRemoveMarkets(int ownerCount, int parallel, IScheduler scheduler) =>
+                        marketFaker.IntervalGenerate(MaxAddTime, scheduler)
+                            .Parallelize(ownerCount, parallel, obs => obs.StressAddRemove(marketCache, _ => GetRemoveTime(), scheduler))
+                            .Finally(marketCache.Dispose);
+
+                    IObservable<MarketPrice> AddRemovePrices(Market market, int priceCount, int parallel, IScheduler scheduler) =>
+                        randomizer.Interval(MaxAddTime, scheduler).Select(_ => market.CreateUniquePrice(_ => GetRandomPrice(randomizer)))
+                            .Parallelize(priceCount, parallel, obs => obs.StressAddRemove(market.PricesCache, _ => GetRemoveTime(), scheduler))
+                            .Finally(market.PricesCache.Dispose);
+                }
+            }
+
+            private static void CheckResultContents(
+                SourceCache<IMarket, Guid> marketCache,
+                ChangeSetAggregator<IMarket, Guid> marketResults,
+                ChangeSetAggregator<MarketPrice, int> priceResults)
+            {
+                var expectedMarkets = marketCache.Items.ToList();
+                var expectedPrices = expectedMarkets.SelectMany(market => ((Market)market).PricesCache.Items).ToList();
+
+                // These should be subsets of each other
+                expectedMarkets.Should().BeSubsetOf(marketResults.Data.Items);
+                marketResults.Data.Items.Count.Should().Be(expectedMarkets.Count);
+
+                // These should be subsets of each other
+                expectedPrices.Should().BeSubsetOf(priceResults.Data.Items);
+                priceResults.Data.Items.Count.Should().Be(expectedPrices.Count);
+            }
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithoutSourceComparer.UnitTests.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithoutSourceComparer.UnitTests.cs
new file mode 100644
index 000000000..6ee493b6d
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithoutSourceComparer.UnitTests.cs
@@ -0,0 +1,887 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reactive.Linq;
+
+using Bogus;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Kernel;
+using DynamicData.Tests.Domain;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForCacheChangeSets
+    {
+        public static partial class WithoutSourceComparer
+        {
+            public class UnitTests
+            {
+                [Fact]
+                public void AbleToInvokeFactory()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    // having
+                    var invoked = false;
+                    IObservable<IChangeSet<MarketPrice, int>> factory(IMarket m)
+                    {
+                        invoked = true;
+                        return m.LatestPrices;
+                    }
+                    using var sub = marketCache.Connect().MergeManyChangeSets(factory).Subscribe();
+
+                    // when
+                    marketCache.AddOrUpdate(new Market(0));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    invoked.Should().BeTrue();
+                }
+
+                [Fact]
+                public void AbleToInvokeFactoryWithKey()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    // having
+                    var invoked = false;
+                    IObservable<IChangeSet<MarketPrice, int>> factory(IMarket m, Guid g)
+                    {
+                        invoked = true;
+                        return m.LatestPrices;
+                    }
+                    using var sub = marketCache.Connect().MergeManyChangeSets(factory).Subscribe();
+
+                    // when
+                    marketCache.AddOrUpdate(new Market(0));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    invoked.Should().BeTrue();
+                }
+
+                [Fact]
+                public void AllExistingSubItemsPresentInResult()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    AddUniquePrices(markets, randomizer);
+
+                    // when
+                    marketCache.AddOrUpdate(markets);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount);
+                    markets.Sum(m => m.PricesCache.Count).Should().Be(MarketCount * PricesPerMarket);
+                    results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
+                    results.Messages.Count.Should().Be(1);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                }
+
+                [Fact]
+                public void AllNewSubItemsPresentInResult()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+
+                    // when
+                    AddUniquePrices(markets, randomizer);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount);
+                    markets.Sum(m => m.PricesCache.Count).Should().Be(MarketCount * PricesPerMarket);
+                    results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
+                    results.Messages.Count.Should().Be(MarketCount);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                }
+
+                [Fact]
+                public void AllRefreshedSubItemsAreRefreshed()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+                    AddUniquePrices(markets, randomizer);
+
+                    // when
+                    markets.ForEach(m => m.RefreshAllPrices(() => GetRandomPrice(randomizer)));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount);
+                    results.Data.Count.Should().Be(MarketCount * PricesPerMarket);
+                    results.Messages.Count.Should().Be(MarketCount * 2);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(MarketCount * PricesPerMarket);
+                }
+
+                [Fact]
+                public void AnyDuplicateKeyValuesShouldBeHidden()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+
+                    // when
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                }
+
+                [Fact]
+                public void AnyDuplicateValuesShouldBeNoOpWhenRemoved()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // when
+                    markets[1].RemoveAllPrices();
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                }
+
+                [Fact]
+                public void AnyDuplicateValuesShouldBeUnhiddenWhenOtherIsRemoved()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // when
+                    marketCache.Remove(markets[0]);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Data.Items.Zip(markets[1].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                    results.Messages.Count.Should().Be(2);
+                    results.Messages[1].Updates.Should().Be(PricesPerMarket);
+                }
+
+                [Fact]
+                public void AnyDuplicateValuesShouldNotRefreshWhenHidden()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, 2).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+                    markets[0].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    markets[1].SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+
+                    // when
+                    markets[1].RefreshAllPrices(() => GetRandomPrice(randomizer));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                    results.Data.Items.Zip(markets[0].PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                }
+
+                [Fact]
+                public void AnyRemovedSubItemIsRemoved()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    marketCache.AddOrUpdate(markets);
+                    AddUniquePrices(markets, randomizer);
+
+                    // when
+                    markets.ForEach(m => m.PricesCache.Edit(updater => updater.RemoveKeys(updater.Keys.Take(RemoveCount))));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount);
+                    results.Data.Count.Should().Be(MarketCount * (PricesPerMarket - RemoveCount));
+                    results.Messages.Count.Should().Be(MarketCount * 2);
+                    results.Messages[0].Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(MarketCount * RemoveCount);
+                }
+
+                [Fact]
+                public void AnySourceItemRemovedRemovesAllSourceValues()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    AddUniquePrices(markets, randomizer);
+                    marketCache.AddOrUpdate(markets);
+
+                    // when
+                    marketCache.Edit(updater => updater.RemoveKeys(updater.Keys.Take(RemoveCount)));
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(MarketCount - RemoveCount);
+                    results.Messages.Count.Should().Be(2);
+                    results.Data.Count.Should().Be((MarketCount - RemoveCount) * PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(PricesPerMarket * RemoveCount);
+                }
+
+                [Fact]
+                public void ChangingSourceByUpdateRemovesPreviousAndAddsNewValues()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    var market = new Market(0);
+                    market.SetPrices(0, PricesPerMarket * 2, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(market);
+                    var updatedMarket = new Market(market);
+                    updatedMarket.SetPrices(PricesPerMarket, PricesPerMarket * 3, () => GetRandomPrice(randomizer));
+
+                    // when
+                    marketCache.AddOrUpdate(updatedMarket);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    results.Data.Count.Should().Be(PricesPerMarket * 2);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket * 3);
+                    results.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(PricesPerMarket);
+                    results.Data.Items.Zip(updatedMarket.PricesCache.Items).ForEach(pair => pair.First.Should().Be(pair.Second));
+                }
+
+                [Fact]
+                public void ClearingParentEmitsSingleChangeSet()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    AddUniquePrices(markets, randomizer);
+                    marketCache.AddOrUpdate(markets);
+
+                    // when
+                    marketCache.Clear();
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(0);
+                    results.Data.Count.Should().Be(0);
+                    results.Messages.Count.Should().Be(2);
+                    results.Summary.Overall.Adds.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(MarketCount * PricesPerMarket);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                }
+
+                [Fact]
+                public void ComparerOnlyAddsBetterAddedValues()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    using var highPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
+                    using var lowPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketLow = new Market(1);
+                    var marketHigh = new Market(2);
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketLow);
+                    marketCache.AddOrUpdate(marketHigh);
+
+                    // when
+                    marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketHigh.SetPrices(0, PricesPerMarket, HighestPrice);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(3);
+                    lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
+                    highPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketHigh.Id));
+                }
+
+                [Fact]
+                public void ComparerOnlyAddsBetterExistingValues()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    using var highPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
+                    using var lowPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketLow = new Market(1);
+                    var marketHigh = new Market(2);
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketHigh.SetPrices(0, PricesPerMarket, HighestPrice);
+
+                    // when
+                    marketCache.AddOrUpdate(marketLow);
+                    marketCache.AddOrUpdate(marketHigh);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(3);
+                    lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
+                    highPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketHigh.Id));
+                }
+
+                [Fact]
+                public void ComparerOnlyAddsBetterValuesOnSourceUpdate()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    using var highPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
+                    using var lowPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketLow = new Market(1);
+                    var marketLowLow = new Market(marketLow);
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketLowLow.SetPrices(0, PricesPerMarket, LowestPrice - 1);
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketLow);
+
+                    // when
+                    marketCache.AddOrUpdate(marketLowLow);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLowLow.Id));
+                    highPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    highPriceResults.Summary.Overall.Updates.Should().Be(0);
+                    highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                }
+
+                [Fact]
+                public void ComparerOnlyRefreshesVisibleValues()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    using var highPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer, MarketPrice.HighPriceCompare).AsAggregator();
+                    using var lowPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer, MarketPrice.LowPriceCompare).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketLow = new Market(1);
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketLow);
+
+                    // when
+                    marketLow.RefreshAllPrices(LowestPrice - 1);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Refreshes.Should().Be(PricesPerMarket);
+                    lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
+                    highPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    highPriceResults.Summary.Overall.Updates.Should().Be(0);
+                    highPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                }
+
+                [Fact]
+                public void ComparerOnlyUpdatesVisibleValuesOnUpdate()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    using var highPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
+                    using var lowPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketLow = new Market(1);
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketLow);
+
+                    // when
+                    marketLow.UpdateAllPrices(LowestPrice - 1);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    lowPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketLow.Id));
+                    highPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    highPriceResults.Summary.Overall.Updates.Should().Be(0);
+                    highPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                }
+
+                [Fact]
+                public void ComparerUpdatesToCorrectValueOnRefresh()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    using var highPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
+                    using var lowPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketFlipFlop = new Market(1);
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketFlipFlop.SetPrices(0, PricesPerMarket, HighestPrice);
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketFlipFlop);
+
+                    // when
+                    marketFlipFlop.RefreshAllPrices(LowestPrice);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketFlipFlop.Id));
+                    highPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    highPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                }
+
+                [Fact]
+                public void ComparerUpdatesToCorrectValueOnRemove()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    using var lowPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
+                    using var highPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketLow = new Market(1);
+                    var marketHigh = new Market(2);
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketLow);
+                    marketCache.AddOrUpdate(marketHigh);
+                    marketLow.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketHigh.SetPrices(0, PricesPerMarket, HighestPrice);
+
+                    // when
+                    marketCache.Remove(marketLow);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                    lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                    highPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketHigh.Id));
+                }
+
+                [Fact]
+                public void ComparerUpdatesToCorrectValueOnUpdate()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    using var highPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.HighPriceCompare).AsAggregator();
+                    using var lowPriceResults = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.LowPriceCompare).AsAggregator();
+                    var marketOriginal = new Market(0);
+                    var marketFlipFlop = new Market(1);
+                    marketOriginal.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer));
+                    marketFlipFlop.SetPrices(0, PricesPerMarket, HighestPrice);
+                    marketCache.AddOrUpdate(marketOriginal);
+                    marketCache.AddOrUpdate(marketFlipFlop);
+
+                    // when
+                    marketFlipFlop.UpdateAllPrices(LowestPrice);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(2);
+                    lowPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    lowPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket);
+                    lowPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    lowPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketFlipFlop.Id));
+                    highPriceResults.Data.Count.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    highPriceResults.Summary.Overall.Removes.Should().Be(0);
+                    highPriceResults.Summary.Overall.Updates.Should().Be(PricesPerMarket * 2);
+                    highPriceResults.Summary.Overall.Refreshes.Should().Be(0);
+                    highPriceResults.Data.Items.Select(cp => cp.MarketId).ForEach(guid => guid.Should().Be(marketOriginal.Id));
+                }
+
+                [Fact]
+                public void EqualityComparerHidesUpdatesWithoutChanges()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+                    using var marketCacheResults = marketCache.Connect().AsAggregator();
+
+                    // having
+                    var market = new Market(0);
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    market.SetPrices(0, PricesPerMarket, LowestPrice);
+                    marketCache.AddOrUpdate(market);
+
+                    // when
+                    market.SetPrices(0, PricesPerMarket, LowestPrice);
+
+                    // then
+                    marketCacheResults.Data.Count.Should().Be(1);
+                    results.Data.Count.Should().Be(PricesPerMarket);
+                    results.Messages.Count.Should().Be(1);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Fact]
+                public void EveryItemVisibleWhenSequenceCompletes()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    marketCache.AddOrUpdate(Enumerable.Range(0, MarketCount).Select(n => new FixedMarket(() => GetRandomPrice(randomizer), n * ItemIdStride, (n * ItemIdStride) + PricesPerMarket)));
+
+                    // when
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices).AsAggregator();
+
+                    marketCache.Items.ForEach(m => (m as IDisposable)?.Dispose());
+                    marketCache.Dispose();
+
+                    // then
+                    results.Data.Count.Should().Be(PricesPerMarket * MarketCount);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket * MarketCount);
+                    results.Summary.Overall.Removes.Should().Be(0);
+                    results.Summary.Overall.Updates.Should().Be(0);
+                    results.Summary.Overall.Refreshes.Should().Be(0);
+                }
+
+                [Theory]
+                [InlineData(false, false)]
+                [InlineData(false, true)]
+                [InlineData(true, false)]
+                [InlineData(true, true)]
+                public void MergedObservableCompletesOnlyWhenSourceAndAllChildrenComplete(bool completeSource, bool completeChildren)
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    marketCache.AddOrUpdate(Enumerable.Range(0, MarketCount).Select(n => new FixedMarket(() => GetRandomPrice(randomizer), n * ItemIdStride, (n * ItemIdStride) + PricesPerMarket, completable: completeChildren)));
+                    var hasSourceSequenceCompleted = false;
+                    var hasMergedSequenceCompleted = false;
+
+                    using var cleanup = marketCache.Connect().Do(_ => { }, () => hasSourceSequenceCompleted = true)
+                        .MergeManyChangeSets(m => m.LatestPrices).Subscribe(_ => { }, () => hasMergedSequenceCompleted = true);
+
+                    // when
+                    if (completeSource)
+                    {
+                        marketCache.Items.ForEach(m => (m as IDisposable)?.Dispose());
+                        marketCache.Dispose();
+                    }
+
+                    // then
+                    hasSourceSequenceCompleted.Should().Be(completeSource);
+                    hasMergedSequenceCompleted.Should().Be(completeSource && completeChildren);
+                }
+
+                [Fact]
+                public void MergedObservableWillFailIfSourceFails()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    marketCache.AddOrUpdate(markets);
+                    var receivedError = default(Exception);
+                    var expectedError = new Exception("Test exception");
+                    var throwObservable = Observable.Throw<IChangeSet<IMarket, Guid>>(expectedError);
+
+                    using var cleanup = marketCache.Connect().Concat(throwObservable)
+                        .MergeManyChangeSets(m => m.LatestPrices).Subscribe(_ => { }, err => receivedError = err);
+
+                    // when
+                    marketCache.Items.ForEach(m => (m as IDisposable)?.Dispose());
+                    marketCache.Dispose();
+
+                    // then
+                    receivedError.Should().Be(expectedError);
+                }
+
+                [Fact]
+                public void MergeManyChangeSetsWorksCorrectlyWithValueTypes()
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // having
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    marketCache.AddOrUpdate(markets);
+                    markets.ForEach(m => m.SetPrices(0, PricesPerMarket, () => GetRandomPrice(randomizer)));
+                    using var results = marketCache.Connect()
+                        .MergeManyChangeSets(m => m.LatestPrices.Transform(p => p.Price))
+                        .AsAggregator();
+
+                    // when
+                    markets.ForEach(m => m.RemoveAllPrices());
+
+                    // then
+                    results.Data.Count.Should().Be(0);
+                    results.Summary.Overall.Adds.Should().Be(PricesPerMarket);
+                    results.Summary.Overall.Removes.Should().Be(PricesPerMarket);
+                }
+
+                [Fact]
+                public void NullChecks()
+                {
+                    // having
+                    var emptyChangeSetObs = Observable.Empty<IChangeSet<int, int>>();
+                    var nullChangeSetObs = (IObservable<IChangeSet<int, int>>)null!;
+                    var emptyChildChangeSetObs = Observable.Empty<IChangeSet<string, string>>();
+                    var emptySelector = new Func<int, IObservable<IChangeSet<string, string>>>(i => emptyChildChangeSetObs);
+                    var emptyKeySelector = new Func<int, int, IObservable<IChangeSet<string, string>>>((i, key) => emptyChildChangeSetObs);
+                    var nullSelector = (Func<int, IObservable<IChangeSet<string, string>>>)null!;
+                    var nullKeySelector = (Func<int, int, IObservable<IChangeSet<string, string>>>)null!;
+                    var nullParentComparer = (IComparer<int>)null!;
+                    var emptyParentComparer = new NoOpComparer<int>() as IComparer<int>;
+                    var nullChildComparer = (IComparer<string>)null!;
+                    var emptyChildComparer = new NoOpComparer<string>() as IComparer<string>;
+                    var nullEqualityComparer = (IEqualityComparer<string>)null!;
+                    var emptyEqualityComparer = new NoOpEqualityComparer<string>() as IEqualityComparer<string>;
+
+                    // when
+                    var actionDefault1 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector);
+                    var actionDefault2a = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector);
+                    var actionDefault2b = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector);
+                    var actionChildCompare1 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector, comparer: emptyChildComparer);
+                    var actionChildCompare2a = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector, comparer: emptyChildComparer);
+                    var actionChildCompare2b = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector, comparer: emptyChildComparer);
+                    var actionChildCompare2c = () => emptyChangeSetObs.MergeManyChangeSets(emptyKeySelector, comparer: nullChildComparer);
+
+                    // then
+                    emptyChangeSetObs.Should().NotBeNull();
+                    emptyChildChangeSetObs.Should().NotBeNull();
+                    emptyChildComparer.Should().NotBeNull();
+                    emptyEqualityComparer.Should().NotBeNull();
+                    emptyKeySelector.Should().NotBeNull();
+                    emptyParentComparer.Should().NotBeNull();
+                    emptySelector.Should().NotBeNull();
+                    nullChangeSetObs.Should().BeNull();
+                    nullChildComparer.Should().BeNull();
+                    nullEqualityComparer.Should().BeNull();
+                    nullKeySelector.Should().BeNull();
+                    nullParentComparer.Should().BeNull();
+                    nullSelector.Should().BeNull();
+
+                    actionDefault1.Should().Throw<ArgumentNullException>();
+                    actionDefault2a.Should().Throw<ArgumentNullException>();
+                    actionDefault2b.Should().Throw<ArgumentNullException>();
+                    actionChildCompare1.Should().Throw<ArgumentNullException>();
+                    actionChildCompare2a.Should().Throw<ArgumentNullException>();
+                    actionChildCompare2b.Should().Throw<ArgumentNullException>();
+                    actionChildCompare2c.Should().Throw<ArgumentNullException>();
+                }
+
+                [Theory]
+                [InlineData(true)]
+                [InlineData(false)]
+                public void OrderOfChangesIsPreserved(bool removeFirst)
+                {
+                    using var marketCache = new SourceCache<IMarket, Guid>(p => p.Id);
+
+                    var randomizer = new Randomizer(0x21123737);
+
+                    // Arrange
+                    var markets = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    AddUniquePrices(markets, randomizer);
+                    marketCache.AddOrUpdate(markets);
+                    var markets2 = Enumerable.Range(0, MarketCount).Select(n => new Market(n)).ToArray();
+                    AddUniquePrices(markets2, randomizer);
+                    using var results = marketCache.Connect().MergeManyChangeSets(m => m.LatestPrices, MarketPrice.EqualityComparer).AsAggregator();
+                    (var firstReason, var nextReason, int expectedChanges) = removeFirst 
+                        ? (ChangeReason.Remove, ChangeReason.Add, 2 * MarketCount * PricesPerMarket)
+                        : (ChangeReason.Add, ChangeReason.Remove, 3 * MarketCount * PricesPerMarket);
+
+                    // Act
+                    marketCache.Edit(updater =>
+                    {
+                        if (removeFirst)
+                        {
+                            updater.Clear();
+                            updater.AddOrUpdate(markets2);
+                        }
+                        else
+                        {
+
+                            updater.AddOrUpdate(markets2);
+                            updater.Clear();
+                        }
+                    });
+
+                    // Assert
+                    results.Messages.Count.Should().Be(2);
+                    results.Messages[0].All(change => change.Reason is ChangeReason.Add).Should().BeTrue();
+                    results.Messages[1].Count.Should().Be(expectedChanges);
+                    results.Messages[1].Take(MarketCount * PricesPerMarket).All(change => change.Reason == firstReason).Should().BeTrue();
+                    results.Messages[1].Skip(MarketCount * PricesPerMarket).All(change => change.Reason == nextReason).Should().BeTrue();
+                }
+
+                private static void AddUniquePrices(
+                        Market[] markets,
+                        Randomizer randomizer)
+                    => markets.ForEach(m => m.AddUniquePrices(PricesPerMarket, _ => GetRandomPrice(randomizer)));
+            }
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithoutSourceComparer.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithoutSourceComparer.cs
new file mode 100644
index 000000000..2a25f0b2c
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.WithoutSourceComparer.cs
@@ -0,0 +1,9 @@
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForCacheChangeSets
+    {
+        public static partial class WithoutSourceComparer;
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.cs
new file mode 100644
index 000000000..dc14907d2
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForCacheChangeSets.cs
@@ -0,0 +1,31 @@
+using Bogus;
+
+using DynamicData.Tests.Domain;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForCacheChangeSets
+    {
+        #if DEBUG
+        private const int MarketCount = 5;
+        private const int PricesPerMarket = 7;
+        private const int RemoveCount = 3;
+        #else
+        private const int MarketCount = 101;
+        private const int PricesPerMarket = 103;
+        private const int RemoveCount = 53;
+        #endif
+
+        private const int ItemIdStride = 1000;
+        private const decimal BasePrice = 10m;
+        private const decimal PriceOffset = 10m;
+        private const decimal HighestPrice = BasePrice + PriceOffset + 1.0m;
+        private const decimal LowestPrice = BasePrice - 1.0m;
+
+        private static decimal GetRandomPrice(Randomizer randomizer)
+            => MarketPrice.RandomPrice(randomizer, BasePrice, PriceOffset);
+
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForListChangesets.IntegrationTests.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForListChangesets.IntegrationTests.cs
new file mode 100644
index 000000000..81b341fb6
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForListChangesets.IntegrationTests.cs
@@ -0,0 +1,116 @@
+using System;
+using System.Reactive;
+using System.Reactive.Concurrency;
+using System.Reactive.Disposables;
+using System.Reactive.Linq;
+using System.Reactive.Threading.Tasks;
+using System.Threading.Tasks;
+
+using Bogus;
+
+using Xunit;
+
+using DynamicData.Tests.Domain;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForListChangesets
+    {
+        public sealed class IntegrationTests
+            : IntegrationTestFixtureBase
+        {
+            [Theory]
+            [InlineData(5, 7)]
+            [InlineData(10, 50)]
+            #if !DEBUG
+            [InlineData(10, 1_000)]
+            [InlineData(200, 500)]
+            [InlineData(1_000, 10)]
+            #endif
+            public async Task MultiThreadedStressTest(int ownerCount, int animalCount)
+            {
+                var MaxAddTime = TimeSpan.FromSeconds(0.250);
+                var MaxRemoveTime = TimeSpan.FromSeconds(0.100);
+
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+
+                var mergeAnimals = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).Publish();
+                var addingAnimals = true;
+                var cacheCompleted = mergeAnimals.LastOrDefaultAsync().ToTask();
+                using var animalResults = mergeAnimals.AsAggregator();
+                using var connect = mergeAnimals.Connect();
+
+                // Start asynchronously modifying the parent list and the child lists
+                using var addAnimals = AddRemoveAnimalsStress(ownerCount, animalCount, Environment.ProcessorCount, TaskPoolScheduler.Default)
+                    .Finally(() => addingAnimals = false)
+                    .Subscribe();
+
+                // Subscribe / unsubscribe over and over while the collections are being modified
+                do
+                {
+                    // Ensure items are being added asynchronously before subscribing to the animal changes
+                    await Task.Yield();
+
+                    {
+                        // Subscribe
+                        var mergedSub = mergeAnimals.Subscribe();
+
+                        // Let other threads run
+                        await Task.Yield();
+
+                        // Unsubscribe
+                        mergedSub.Dispose();
+                    }
+                }
+                while (addingAnimals);
+
+                // Wait for the source cache to finish delivering all notifications.
+                await cacheCompleted;
+
+                // Verify the results against the aggregator wired into the same Publish chain
+                // that cacheCompleted observes.
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+
+
+                TimeSpan? GetRemoveTime() => randomizer.Bool() ? randomizer.TimeSpan(MaxRemoveTime) : null;
+
+                IObservable<Unit> AddRemoveAnimalsStress(int ownerCount, int animalCount, int parallel, IScheduler scheduler) =>
+                    Observable.Create<Unit>(observer => new CompositeDisposable
+                    (
+                        AddRemoveOwners(ownerCount, parallel, scheduler)
+                            .Subscribe(
+                                onNext: static _ => { },
+                                onError: observer.OnError),
+
+                        animalOwners.Connect()
+                            .MergeMany(owner => AddRemoveAnimals(owner, animalCount, parallel, scheduler))
+                            .Subscribe(
+                                onNext: static _ => { },
+                                onError: observer.OnError,
+                                onCompleted: observer.OnCompleted)
+                    ));
+
+                IObservable<AnimalOwner> AddRemoveOwners(int ownerCount, int parallel, IScheduler scheduler) =>
+                    animalOwnerFaker.IntervalGenerate(randomizer, MaxAddTime, scheduler)
+                        .Parallelize(ownerCount, parallel, obs => obs.StressAddRemove(animalOwners, _ => GetRemoveTime(), scheduler))
+                        .Finally(animalOwners.Dispose);
+
+                IObservable<Animal> AddRemoveAnimals(AnimalOwner owner, int animalCount, int parallel, IScheduler scheduler) =>
+                    animalFaker.IntervalGenerate(randomizer, MaxAddTime, scheduler)
+                        .Parallelize(animalCount, parallel, obs => obs.StressAddRemove(owner.Animals, _ => GetRemoveTime(), scheduler))
+                        .Finally(owner.Animals.Dispose);
+            }
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForListChangesets.UnitTests.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForListChangesets.UnitTests.cs
new file mode 100644
index 000000000..240cd2111
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForListChangesets.UnitTests.cs
@@ -0,0 +1,540 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reactive.Linq;
+
+using Bogus;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Kernel;
+using DynamicData.Tests.Domain;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForListChangesets
+    {
+        public class UnitTests
+        {
+            [Fact]
+            public void NullChecks()
+            {
+                // Arrange
+                var emptyChangeSetObs = Observable.Empty<IChangeSet<int, int>>();
+                var nullChangeSetObs = (IObservable<IChangeSet<int, int>>)null!;
+                var emptyKeySelector = new Func<int, int, IObservable<IChangeSet<string>>>((_, _) => Observable.Empty<IChangeSet<string>>());
+                var nullKeySelector = (Func<int, int, IObservable<IChangeSet<string>>>)null!;
+                var emptySelector = new Func<int, IObservable<IChangeSet<string>>>(i => Observable.Empty<IChangeSet<string>>());
+                var nullSelector = (Func<int, IObservable<IChangeSet<string>>>)null!;
+
+                // Act
+                var checkParam1 = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector);
+                var checkParam2 = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector);
+                var checkParam3 = () => nullChangeSetObs.MergeManyChangeSets(emptySelector);
+                var checkParam4 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector);
+
+                // Assert
+                emptyChangeSetObs.Should().NotBeNull();
+                emptyKeySelector.Should().NotBeNull();
+                emptySelector.Should().NotBeNull();
+                nullChangeSetObs.Should().BeNull();
+                nullKeySelector.Should().BeNull();
+                nullSelector.Should().BeNull();
+
+                checkParam1.Should().Throw<ArgumentNullException>();
+                checkParam2.Should().Throw<ArgumentNullException>();
+                checkParam3.Should().Throw<ArgumentNullException>();
+                checkParam4.Should().Throw<ArgumentNullException>();
+            }
+
+            [Theory]
+            [InlineData(false, false)]
+            [InlineData(false, true)]
+            [InlineData(true, false)]
+            [InlineData(true, true)]
+            public void ResultCompletesOnlyWhenSourceAndAllChildrenComplete(bool completeSource, bool completeChildren)
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                // Act
+                animalOwners.Items.Skip(completeChildren ? 0 : 1).ForEach(owner => owner.Dispose());
+                if (completeSource)
+                {
+                    animalOwners.Dispose();
+                }
+
+                // Assert
+                animalOwnerResults.IsCompleted.Should().Be(completeSource);
+                animalResults.IsCompleted.Should().Be(completeSource && completeChildren);
+            }
+
+            [Fact]
+            public void ResultContainsAllInitialChildren()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                // Act
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
+                animalResults.Messages.Count.Should().Be(1);
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultContainsChildrenFromAddedParents()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var addThis = animalOwnerFaker.Generate();
+
+                // Act
+                animalOwners.AddOrUpdate(addThis);
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount + 1);
+                animalResults.Messages.Count.Should().Be(2);
+                addThis.Animals.Items.ForEach(added => animalResults.Data.Items.Should().Contain(added));
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultContainsChildrenAddedWithAddRange()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var initialCount = animalOwners.Items.Sum(owner => owner.Animals.Count);
+                var totalAdded = new List<Animal>();
+
+                // Act
+                animalOwners.Items.ForEach(owner => owner.Animals.AddRange(animalFaker.Generate(AddRangeSize).With(added => totalAdded.AddRange(added))));
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
+                animalResults.Messages.Count.Should().Be(1 + InitialOwnerCount); // Initial + 1 for each Range Added
+                totalAdded.ForEach(animal => animalResults.Data.Items.Should().Contain(animal));
+                animalOwners.Items.Sum(owner => owner.Animals.Count).Should().Be(initialCount + totalAdded.Count);
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultContainsChildrenAddedWithInsert()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var randomOwner = randomizer.ListItem(animalOwners.Items.ToList());
+                var insertIndex = randomizer.Number(randomOwner.Animals.Items.Count);
+                var insertThis = animalFaker.Generate();
+                var initialCount = animalOwners.Items.Sum(owner => owner.Animals.Count);
+
+                // Act
+                randomOwner.Animals.Insert(insertIndex, insertThis);
+
+                // Assert
+                randomOwner.Animals.Items.ElementAt(insertIndex).Should().Be(insertThis);
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
+                animalResults.Messages.Count.Should().Be(2);
+                animalResults.Data.Items.Should().Contain(insertThis);
+                animalOwners.Items.Sum(owner => owner.Animals.Count).Should().Be(initialCount + 1);
+                
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultContainsCorrectItemsAfterChildClear()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var randomOwner = randomizer.ListItem(animalOwners.Items.ToList());
+                var removedAnimals = randomOwner.Animals.Items.ToList();
+
+                // Act
+                randomOwner.Animals.Clear();
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
+                animalResults.Messages.Count.Should().Be(2);
+                randomOwner.Animals.Count.Should().Be(0);
+                removedAnimals.ForEach(removed => animalResults.Data.Items.Should().NotContain(removed));
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultContainsCorrectItemsAfterChildReplacement()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var randomOwner = randomizer.ListItem(animalOwners.Items.ToList());
+                var replaceThis = randomizer.ListItem(randomOwner.Animals.Items.ToList());
+                var withThis = animalFaker.Generate();
+
+                // Act
+                randomOwner.Animals.Replace(replaceThis, withThis);
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
+                animalResults.Messages.Count.Should().Be(2);
+                randomOwner.Animals.Items.Should().NotContain(replaceThis);
+                randomOwner.Animals.Items.Should().Contain(withThis);
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultContainsCorrectItemsAfterParentUpdate()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var replaceThis = randomizer.ListItem(animalOwners.Items.ToList());
+                var withThis = CreateWithSameId(animalOwnerFaker, replaceThis);
+
+                // Act
+                animalOwners.AddOrUpdate(withThis);
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount); // Owner Count should not change
+                animalResults.Messages.Count.Should().Be(2); // 2 = Initial Add and one changeset with remove old items / add new items
+                replaceThis.Animals.Items.ForEach(removed => animalResults.Data.Items.Should().NotContain(removed));
+                withThis.Animals.Items.ForEach(added => animalResults.Data.Items.Should().Contain(added));
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+
+                replaceThis.Dispose();
+            }
+
+            [Fact]
+            public void ResultDoesNotContainChildrenFromParentsBatchRemoved()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var removeThese = randomizer.ListItems(animalOwners.Items.ToList(), RemoveRangeSize);
+
+                // Act
+                animalOwners.Remove(removeThese);
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount - RemoveRangeSize);
+                animalResults.Messages.Count.Should().Be(2);
+                removeThese.SelectMany(owner => owner.Animals.Items).ForEach(removed => animalResults.Data.Items.Should().NotContain(removed));
+                
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+                
+                removeThese.ForEach(owner => owner.Dispose());
+            }
+
+            [Fact]
+            public void ResultDoesNotContainChildrenFromParentsRemovedWithRemove()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var removeThis = randomizer.ListItem(animalOwners.Items.ToList());
+
+                // Act
+                animalOwners.Remove(removeThis);
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount - 1);
+                animalResults.Messages.Count.Should().Be(2);
+                removeThis.Animals.Items.ForEach(removed => animalResults.Data.Items.Should().NotContain(removed));
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+
+                removeThis.Dispose();
+            }
+
+            [Fact]
+            public void ResultDoesNotContainChildrenRemovedWithRemove()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var randomOwner = randomizer.ListItem(animalOwners.Items.ToList());
+                var removeThis = randomizer.ListItem(randomOwner.Animals.Items.ToList());
+                var initialCount = animalOwners.Items.Sum(owner => owner.Animals.Count);
+
+                // Act
+                randomOwner.Animals.Remove(removeThis);
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
+                animalResults.Messages.Count.Should().Be(2);
+                animalResults.Data.Items.Should().NotContain(removeThis);
+                animalOwners.Items.Sum(owner => owner.Animals.Count).Should().Be(initialCount - 1);
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultDoesNotContainChildrenRemovedWithRemoveAt()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var randomOwner = randomizer.ListItem(animalOwners.Items.ToList());
+                var removeIndex = randomizer.Number(randomOwner.Animals.Count - 1);
+                var removeThis = randomOwner.Animals.Items.ElementAt(removeIndex);
+                var initialCount = animalOwners.Items.Sum(owner => owner.Animals.Count);
+
+                // Act
+                randomOwner.Animals.RemoveAt(removeIndex);
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
+                animalResults.Messages.Count.Should().Be(2);
+                animalResults.Data.Items.Should().NotContain(removeThis);
+                animalOwners.Items.Sum(owner => owner.Animals.Count).Should().Be(initialCount - 1);
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultDoesNotContainChildrenRemovedWithRemoveMany()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var randomOwner = randomizer.ListItem(animalOwners.Items.ToList());
+                var removeCount = randomizer.Number(1, randomOwner.Animals.Count - 1);
+                var removeThese = randomizer.ListItems(randomOwner.Animals.Items.ToList(), removeCount);
+
+                // Act
+                randomOwner.Animals.RemoveMany(removeThese);
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
+                animalResults.Messages.Count.Should().Be(2);
+                removeThese.ForEach(removed => randomOwner.Animals.Items.Should().NotContain(removed));
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultDoesNotContainChildrenRemovedWithRemoveRange()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var randomOwner = randomizer.ListItem(animalOwners.Items.ToList());
+                var removeCount = randomizer.Number(1, randomOwner.Animals.Count - 1);
+                var removeIndex = randomizer.Number(randomOwner.Animals.Count - removeCount - 1);
+                var removeThese = randomOwner.Animals.Items.Skip(removeIndex).Take(removeCount);
+
+                // Act
+                randomOwner.Animals.RemoveRange(removeIndex, removeCount);
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
+                animalResults.Messages.Count.Should().Be(2);
+                removeThese.ForEach(removed => randomOwner.Animals.Items.Should().NotContain(removed));
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+            }
+
+            [Fact]
+            public void ResultEmptyIfSourceIsCleared()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                using var animalOwnerResults = animalOwners.Connect().AsAggregator();
+                using var animalResults = animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                var items = animalOwners.Items.ToList();
+
+                // Act
+                animalOwners.Clear();
+
+                // Assert
+                animalOwnerResults.Data.Count.Should().Be(0);
+                animalResults.Data.Count.Should().Be(0);
+
+                CheckResultContents(animalOwners.Items, animalOwnerResults, animalResults);
+
+                items.ForEach(owner => owner.Dispose());
+            }
+
+            [Fact]
+            public void ResultFailsIfSourceFails()
+            {
+                using var animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
+                
+                var randomizer = new Randomizer(0x01221948);
+                var animalFaker = Fakers.Animal.Clone().WithSeed(randomizer);
+                var animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(randomizer).WithInitialAnimals(animalFaker);
+
+                // Arrange
+                animalOwners.AddOrUpdate(animalOwnerFaker.Generate(InitialOwnerCount));
+
+                var expectedError = new Exception("Expected");
+                var throwObservable = Observable.Throw<IChangeSet<AnimalOwner, Guid>>(expectedError);
+                using var results = animalOwners.Connect().Concat(throwObservable).MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
+
+                // Act
+                animalOwners.Dispose();
+
+                // Assert
+                results.Exception.Should().Be(expectedError);
+            }
+
+            private static AnimalOwner CreateWithSameId(
+                Faker<AnimalOwner> animalOwnerFaker,
+                AnimalOwner original)
+            {
+                var newOwner = animalOwnerFaker.Generate();
+                var sameId = new AnimalOwner(newOwner.Name, original.Id);
+                sameId.Animals.AddRange(newOwner.Animals.Items);
+                return sameId;
+            }
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForListChangesets.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForListChangesets.cs
new file mode 100644
index 000000000..296474d5c
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.ForListChangesets.cs
@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+using FluentAssertions;
+
+using DynamicData.Tests.Domain;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture
+{
+    public static partial class ForListChangesets
+    {
+        #if DEBUG
+        private const int InitialOwnerCount = 7;
+        private const int AddRangeSize = 5;
+        private const int RemoveRangeSize = 3;
+        #else
+        private const int InitialOwnerCount = 103;
+        private const int AddRangeSize = 53;
+        private const int RemoveRangeSize = 37;
+        #endif
+
+        private static void CheckResultContents(
+            IReadOnlyList<AnimalOwner> owners,
+            ChangeSetAggregator<AnimalOwner, Guid> ownerResults,
+            ChangeSetAggregator<Animal> animalResults)
+        {
+            var expectedOwners = owners.ToList();
+
+            // These should be subsets of each other
+            expectedOwners.Should().BeSubsetOf(ownerResults.Data.Items);
+            ownerResults.Data.Items.Count.Should().Be(expectedOwners.Count);
+
+            // All owner animals should be in the results
+            foreach (var owner in owners)
+            {
+                owner.Animals.Items.Should().BeSubsetOf(animalResults.Data.Items);
+            }
+
+            // Results should not have more than the total number of animals
+            animalResults.Data.Count.Should().Be(owners.Sum(owner => owner.Animals.Count));
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.cs
new file mode 100644
index 000000000..5887b6d61
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/MergeManyChangeSetsFixture.cs
@@ -0,0 +1,3 @@
+namespace DynamicData.Tests.Cache;
+
+public static partial class MergeManyChangeSetsFixture;
diff --git a/src/DynamicData.Tests/Cache/MergeManyChangeSetsListFixture.cs b/src/DynamicData.Tests/Cache/MergeManyChangeSetsListFixture.cs
deleted file mode 100644
index 49f566907..000000000
--- a/src/DynamicData.Tests/Cache/MergeManyChangeSetsListFixture.cs
+++ /dev/null
@@ -1,480 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Reactive;
-using System.Reactive.Concurrency;
-using System.Reactive.Disposables;
-using System.Reactive.Linq;
-using System.Reactive.Threading.Tasks;
-using System.Threading.Tasks;
-using Bogus;
-using DynamicData.Kernel;
-using DynamicData.Tests.Domain;
-using DynamicData.Tests.Utilities;
-using FluentAssertions;
-using Xunit;
-
-namespace DynamicData.Tests.Cache;
-
-public sealed class MergeManyChangeSetsListFixture : IDisposable
-{
-#if DEBUG
-    const int InitialOwnerCount = 7;
-    const int AddRangeSize = 5;
-    const int RemoveRangeSize = 3;
-#else
-    const int InitialOwnerCount = 103;
-    const int AddRangeSize = 53;
-    const int RemoveRangeSize = 37;
-#endif
-
-    private readonly ISourceCache<AnimalOwner, Guid> _animalOwners = new SourceCache<AnimalOwner, Guid>(o => o.Id);
-    private readonly ChangeSetAggregator<AnimalOwner, Guid> _animalOwnerResults;
-    private readonly ChangeSetAggregator<Animal> _animalResults;
-    private readonly Faker<AnimalOwner> _animalOwnerFaker;
-    private readonly Faker<Animal> _animalFaker;
-    private readonly Randomizer _randomizer;
-
-    public MergeManyChangeSetsListFixture()
-    {
-        _randomizer = new Randomizer(0x01221948);
-        _animalFaker = Fakers.Animal.Clone().WithSeed(_randomizer);
-        _animalOwnerFaker = Fakers.AnimalOwner.Clone().WithSeed(_randomizer).WithInitialAnimals(_animalFaker);
-        _animalOwners.AddOrUpdate(_animalOwnerFaker.Generate(InitialOwnerCount));
-
-        _animalOwnerResults = _animalOwners.Connect().AsAggregator();
-        _animalResults = _animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
-    }
-
-    [Theory]
-    [InlineData(5, 7)]
-    [InlineData(10, 50)]
-#if !DEBUG
-    [InlineData(10, 1_000)]
-    [InlineData(200, 500)]
-    [InlineData(1_000, 10)]
-#endif
-    public async Task MultiThreadedStressTest(int ownerCount, int animalCount)
-    {
-        var MaxAddTime = TimeSpan.FromSeconds(0.250);
-        var MaxRemoveTime = TimeSpan.FromSeconds(0.100);
-
-        TimeSpan? GetRemoveTime() => _randomizer.Bool() ? _randomizer.TimeSpan(MaxRemoveTime) : null;
-
-        IObservable<Unit> AddRemoveAnimalsStress(int ownerCount, int animalCount, int parallel, IScheduler scheduler) =>
-            Observable.Create<Unit>(observer => new CompositeDisposable
-                (
-                    AddRemoveOwners(ownerCount, parallel, scheduler)
-                        .Subscribe(
-                            onNext: static _ => { },
-                            onError: observer.OnError),
-
-                    _animalOwners.Connect()
-                        .MergeMany(owner => AddRemoveAnimals(owner, animalCount, parallel, scheduler))
-                        .Subscribe(
-                            onNext: static _ => { },
-                            onError: observer.OnError,
-                            onCompleted: observer.OnCompleted)
-                ));
-
-        IObservable<AnimalOwner> AddRemoveOwners(int ownerCount, int parallel, IScheduler scheduler) =>
-            _animalOwnerFaker.IntervalGenerate(_randomizer, MaxAddTime, scheduler)
-                .Parallelize(ownerCount, parallel, obs => obs.StressAddRemove(_animalOwners, _ => GetRemoveTime(), scheduler))
-                .Finally(_animalOwners.Dispose);
-
-        IObservable<Animal> AddRemoveAnimals(AnimalOwner owner, int animalCount, int parallel, IScheduler scheduler) =>
-            _animalFaker.IntervalGenerate(_randomizer, MaxAddTime, scheduler)
-                .Parallelize(animalCount, parallel, obs => obs.StressAddRemove(owner.Animals, _ => GetRemoveTime(), scheduler))
-                .Finally(owner.Animals.Dispose);
-
-        var mergeAnimals = _animalOwners.Connect().MergeManyChangeSets(owner => owner.Animals.Connect()).Publish();
-        var addingAnimals = true;
-        var cacheCompleted = mergeAnimals.LastOrDefaultAsync().ToTask();
-        using var animalResults = mergeAnimals.AsAggregator();
-        using var connect = mergeAnimals.Connect();
-
-        // Start asynchrononously modifying the parent list and the child lists
-        using var addAnimals = AddRemoveAnimalsStress(ownerCount, animalCount, Environment.ProcessorCount, TaskPoolScheduler.Default)
-            .Finally(() => addingAnimals = false)
-            .Subscribe();
-
-        // Subscribe / unsubscribe over and over while the collections are being modified
-        do
-        {
-            // Ensure items are being added asynchronously before subscribing to the animal changes
-            await Task.Yield();
-
-            {
-                // Subscribe
-                var mergedSub = mergeAnimals.Subscribe();
-
-                // Let other threads run
-                await Task.Yield();
-
-                // Unsubscribe
-                mergedSub.Dispose();
-            }
-        }
-        while (addingAnimals);
-
-        // Wait for the source cache to finish delivering all notifications.
-        await cacheCompleted;
-
-        // Verify the results against the aggregator wired into the same Publish chain
-        // that cacheCompleted observes.
-        CheckResultContents(_animalOwners.Items, _animalOwnerResults, animalResults);
-    }
-
-    [Fact]
-    public void NullChecks()
-    {
-        // Arrange
-        var emptyChangeSetObs = Observable.Empty<IChangeSet<int, int>>();
-        var nullChangeSetObs = (IObservable<IChangeSet<int, int>>)null!;
-        var emptyKeySelector = new Func<int, int, IObservable<IChangeSet<string>>>((_, _) => Observable.Empty<IChangeSet<string>>());
-        var nullKeySelector = (Func<int, int, IObservable<IChangeSet<string>>>)null!;
-        var emptySelector = new Func<int, IObservable<IChangeSet<string>>>(i => Observable.Empty<IChangeSet<string>>());
-        var nullSelector = (Func<int, IObservable<IChangeSet<string>>>)null!;
-
-        // Act
-        var checkParam1 = () => nullChangeSetObs.MergeManyChangeSets(emptyKeySelector);
-        var checkParam2 = () => emptyChangeSetObs.MergeManyChangeSets(nullKeySelector);
-        var checkParam3 = () => nullChangeSetObs.MergeManyChangeSets(emptySelector);
-        var checkParam4 = () => emptyChangeSetObs.MergeManyChangeSets(nullSelector);
-
-        // Assert
-        emptyChangeSetObs.Should().NotBeNull();
-        emptyKeySelector.Should().NotBeNull();
-        emptySelector.Should().NotBeNull();
-        nullChangeSetObs.Should().BeNull();
-        nullKeySelector.Should().BeNull();
-        nullSelector.Should().BeNull();
-
-        checkParam1.Should().Throw<ArgumentNullException>();
-        checkParam2.Should().Throw<ArgumentNullException>();
-        checkParam3.Should().Throw<ArgumentNullException>();
-        checkParam4.Should().Throw<ArgumentNullException>();
-    }
-
-    [Fact]
-    public void ResultContainsAllInitialChildren()
-    {
-        // Arrange
-
-        // Act
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
-        _animalResults.Messages.Count.Should().Be(1);
-        CheckResultContents();
-    }
-
-    [Fact]
-    public void ResultContainsChildrenFromAddedParents()
-    {
-        // Arrange
-        var addThis = _animalOwnerFaker.Generate();
-
-        // Act
-        _animalOwners.AddOrUpdate(addThis);
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount + 1);
-        _animalResults.Messages.Count.Should().Be(2);
-        addThis.Animals.Items.ForEach(added => _animalResults.Data.Items.Should().Contain(added));
-        CheckResultContents();
-    }
-
-    [Fact]
-    public void ResultDoesNotContainChildrenFromParentsRemovedWithRemove()
-    {
-        // Arrange
-        var removeThis = _randomizer.ListItem(_animalOwners.Items.ToList());
-
-        // Act
-        _animalOwners.Remove(removeThis);
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount - 1);
-        _animalResults.Messages.Count.Should().Be(2);
-        removeThis.Animals.Items.ForEach(removed => _animalResults.Data.Items.Should().NotContain(removed));
-        CheckResultContents();
-        removeThis.Dispose();
-    }
-
-    [Fact]
-    public void ResultDoesNotContainChildrenFromParentsBatchRemoved()
-    {
-        // Arrange
-        var removeThese = _randomizer.ListItems(_animalOwners.Items.ToList(), RemoveRangeSize);
-
-        // Act
-        _animalOwners.Remove(removeThese);
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount - RemoveRangeSize);
-        _animalResults.Messages.Count.Should().Be(2);
-        removeThese.SelectMany(owner => owner.Animals.Items).ForEach(removed => _animalResults.Data.Items.Should().NotContain(removed));
-        CheckResultContents();
-        removeThese.ForEach(owner => owner.Dispose());
-    }
-
-    [Fact]
-    public void ResultContainsCorrectItemsAfterParentUpdate()
-    {
-        // Arrange
-        var replaceThis = _randomizer.ListItem(_animalOwners.Items.ToList());
-        var withThis = CreateWithSameId(replaceThis);
-
-        // Act
-        _animalOwners.AddOrUpdate(withThis);
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount); // Owner Count should not change
-        _animalResults.Messages.Count.Should().Be(2); // 2 = Initial Add and one changeset with remove old items / add new items
-        replaceThis.Animals.Items.ForEach(removed => _animalResults.Data.Items.Should().NotContain(removed));
-        withThis.Animals.Items.ForEach(added => _animalResults.Data.Items.Should().Contain(added));
-        CheckResultContents();
-        replaceThis.Dispose();
-    }
-
-    [Fact]
-    public void ResultEmptyIfSourceIsCleared()
-    {
-        // Arrange
-        var items = _animalOwners.Items.ToList();
-
-        // Act
-        _animalOwners.Clear();
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(0);
-        _animalResults.Data.Count.Should().Be(0);
-        CheckResultContents();
-        items.ForEach(owner => owner.Dispose());
-    }
-
-    [Fact]
-    public void ResultContainsChildrenAddedWithAddRange()
-    {
-        // Arrange
-        var initialCount = _animalOwners.Items.Sum(owner => owner.Animals.Count);
-        var totalAdded = new List<Animal>();
-
-        // Act
-        _animalOwners.Items.ForEach(owner => owner.Animals.AddRange(_animalFaker.Generate(AddRangeSize).With(added => totalAdded.AddRange(added))));
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
-        _animalResults.Messages.Count.Should().Be(1 + InitialOwnerCount); // Initial + 1 for each Range Added
-        totalAdded.ForEach(animal => _animalResults.Data.Items.Should().Contain(animal));
-        _animalOwners.Items.Sum(owner => owner.Animals.Count).Should().Be(initialCount + totalAdded.Count);
-        CheckResultContents();
-    }
-
-    [Fact]
-    public void ResultContainsChildrenAddedWithInsert()
-    {
-        // Arrange
-        var randomOwner = _randomizer.ListItem(_animalOwners.Items.ToList());
-        var insertIndex = _randomizer.Number(randomOwner.Animals.Items.Count);
-        var insertThis = _animalFaker.Generate();
-        var initialCount = _animalOwners.Items.Sum(owner => owner.Animals.Count);
-
-        // Act
-        randomOwner.Animals.Insert(insertIndex, insertThis);
-
-        // Assert
-        randomOwner.Animals.Items.ElementAt(insertIndex).Should().Be(insertThis);
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
-        _animalResults.Messages.Count.Should().Be(2);
-        _animalResults.Data.Items.Should().Contain(insertThis);
-        _animalOwners.Items.Sum(owner => owner.Animals.Count).Should().Be(initialCount + 1);
-        CheckResultContents();
-    }
-
-    [Fact]
-    public void ResultDoesNotContainChildrenRemovedWithRemove()
-    {
-        // Arrange
-        var randomOwner = _randomizer.ListItem(_animalOwners.Items.ToList());
-        var removeThis = _randomizer.ListItem(randomOwner.Animals.Items.ToList());
-        var initialCount = _animalOwners.Items.Sum(owner => owner.Animals.Count);
-
-        // Act
-        randomOwner.Animals.Remove(removeThis);
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
-        _animalResults.Messages.Count.Should().Be(2);
-        _animalResults.Data.Items.Should().NotContain(removeThis);
-        _animalOwners.Items.Sum(owner => owner.Animals.Count).Should().Be(initialCount - 1);
-        CheckResultContents();
-    }
-
-    [Fact]
-    public void ResultDoesNotContainChildrenRemovedWithRemoveAt()
-    {
-        // Arrange
-        var randomOwner = _randomizer.ListItem(_animalOwners.Items.ToList());
-        var removeIndex = _randomizer.Number(randomOwner.Animals.Count - 1);
-        var removeThis = randomOwner.Animals.Items.ElementAt(removeIndex);
-        var initialCount = _animalOwners.Items.Sum(owner => owner.Animals.Count);
-
-        // Act
-        randomOwner.Animals.RemoveAt(removeIndex);
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
-        _animalResults.Messages.Count.Should().Be(2);
-        _animalResults.Data.Items.Should().NotContain(removeThis);
-        _animalOwners.Items.Sum(owner => owner.Animals.Count).Should().Be(initialCount - 1);
-        CheckResultContents();
-    }
-
-    [Fact]
-    public void ResultDoesNotContainChildrenRemovedWithRemoveRange()
-    {
-        // Arrange
-        var randomOwner = _randomizer.ListItem(_animalOwners.Items.ToList());
-        var removeCount = _randomizer.Number(1, randomOwner.Animals.Count - 1);
-        var removeIndex = _randomizer.Number(randomOwner.Animals.Count - removeCount - 1);
-        var removeThese = randomOwner.Animals.Items.Skip(removeIndex).Take(removeCount);
-
-        // Act
-        randomOwner.Animals.RemoveRange(removeIndex, removeCount);
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
-        _animalResults.Messages.Count.Should().Be(2);
-        removeThese.ForEach(removed => randomOwner.Animals.Items.Should().NotContain(removed));
-        CheckResultContents();
-    }
-
-    [Fact]
-    public void ResultDoesNotContainChildrenRemovedWithRemoveMany()
-    {
-        // Arrange
-        var randomOwner = _randomizer.ListItem(_animalOwners.Items.ToList());
-        var removeCount = _randomizer.Number(1, randomOwner.Animals.Count - 1);
-        var removeThese = _randomizer.ListItems(randomOwner.Animals.Items.ToList(), removeCount);
-
-        // Act
-        randomOwner.Animals.RemoveMany(removeThese);
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
-        _animalResults.Messages.Count.Should().Be(2);
-        removeThese.ForEach(removed => randomOwner.Animals.Items.Should().NotContain(removed));
-        CheckResultContents();
-    }
-
-    [Fact]
-    public void ResultContainsCorrectItemsAfterChildReplacement()
-    {
-        // Arrange
-        var randomOwner = _randomizer.ListItem(_animalOwners.Items.ToList());
-        var replaceThis = _randomizer.ListItem(randomOwner.Animals.Items.ToList());
-        var withThis = _animalFaker.Generate();
-
-        // Act
-        randomOwner.Animals.Replace(replaceThis, withThis);
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
-        _animalResults.Messages.Count.Should().Be(2);
-        randomOwner.Animals.Items.Should().NotContain(replaceThis);
-        randomOwner.Animals.Items.Should().Contain(withThis);
-        CheckResultContents();
-    }
-
-    [Fact]
-    public void ResultContainsCorrectItemsAfterChildClear()
-    {
-        // Arrange
-        var randomOwner = _randomizer.ListItem(_animalOwners.Items.ToList());
-        var removedAnimals = randomOwner.Animals.Items.ToList();
-
-        // Act
-        randomOwner.Animals.Clear();
-
-        // Assert
-        _animalOwnerResults.Data.Count.Should().Be(InitialOwnerCount);
-        _animalResults.Messages.Count.Should().Be(2);
-        randomOwner.Animals.Count.Should().Be(0);
-        removedAnimals.ForEach(removed => _animalResults.Data.Items.Should().NotContain(removed));
-        CheckResultContents();
-    }
-
-    [Theory]
-    [InlineData(false, false)]
-    [InlineData(false, true)]
-    [InlineData(true, false)]
-    [InlineData(true, true)]
-    public void ResultCompletesOnlyWhenSourceAndAllChildrenComplete(bool completeSource, bool completeChildren)
-    {
-        // Arrange
-
-        // Act
-        _animalOwners.Items.Skip(completeChildren ? 0 : 1).ForEach(owner => owner.Dispose());
-        if (completeSource)
-        {
-            _animalOwners.Dispose();
-        }
-
-        // Assert
-        _animalOwnerResults.IsCompleted.Should().Be(completeSource);
-        _animalResults.IsCompleted.Should().Be(completeSource && completeChildren);
-    }
-
-    [Fact]
-    public void ResultFailsIfSourceFails()
-    {
-        // Arrange
-        var expectedError = new Exception("Expected");
-        var throwObservable = Observable.Throw<IChangeSet<AnimalOwner, Guid>>(expectedError);
-        using var results = _animalOwners.Connect().Concat(throwObservable).MergeManyChangeSets(owner => owner.Animals.Connect()).AsAggregator();
-
-        // Act
-        _animalOwners.Dispose();
-
-        // Assert
-        results.Exception.Should().Be(expectedError);
-    }
-
-    public void Dispose()
-    {
-        _animalOwners.Items.ForEach(owner => owner.Dispose());
-        _animalOwnerResults.Dispose();
-        _animalResults.Dispose();
-        _animalOwners.Dispose();
-    }
-
-    private AnimalOwner CreateWithSameId(AnimalOwner original)
-    {
-        var newOwner = _animalOwnerFaker.Generate();
-        var sameId = new AnimalOwner(newOwner.Name, original.Id);
-        sameId.Animals.AddRange(newOwner.Animals.Items);
-        return sameId;
-    }
-
-    private void CheckResultContents() => CheckResultContents(_animalOwners.Items, _animalOwnerResults, _animalResults);
-
-    private static void CheckResultContents(IEnumerable<AnimalOwner> owners, ChangeSetAggregator<AnimalOwner, Guid> ownerResults, ChangeSetAggregator<Animal> animalResults)
-    {
-        var expectedOwners = owners.ToList();
-
-        // These should be subsets of each other
-        expectedOwners.Should().BeSubsetOf(ownerResults.Data.Items);
-        ownerResults.Data.Items.Count.Should().Be(expectedOwners.Count);
-
-        // All owner animals should be in the results
-        foreach (var owner in owners)
-        {
-            owner.Animals.Items.Should().BeSubsetOf(animalResults.Data.Items);
-        }
-
-        // Results should not have more than the total number of animals
-        animalResults.Data.Count.Should().Be(owners.Sum(owner => owner.Animals.Count));
-    }
-}
diff --git a/src/DynamicData.Tests/Cache/SourceCacheFixture.IntegrationTests.cs b/src/DynamicData.Tests/Cache/SourceCacheFixture.IntegrationTests.cs
new file mode 100644
index 000000000..4aaf9d5ac
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/SourceCacheFixture.IntegrationTests.cs
@@ -0,0 +1,179 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+
+using FluentAssertions;
+
+using Xunit;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class SourceCacheFixture
+{
+    public sealed class IntegrationTests
+        : IntegrationTestFixtureBase
+    {
+        [Fact]
+        public void ConnectDuringDeliveryDoesNotDuplicate()
+        {
+            // Exploits the dequeue-to-OnNext window. Thread A writes two items in
+            // separate batches. The first delivery is held by a slow subscriber.
+            // While item1 delivery is blocked, item2 is committed to ReaderWriter
+            // and sitting in the queue. Thread B calls Connect(), takes a snapshot
+            // (sees both items), subscribes to _changes, then item2 is delivered
+            // via OnNext — producing a duplicate if not guarded by a generation counter.
+            using var cache = new SourceCache<TestItem, string>(static x => x.Key);
+
+            using var delivering = new ManualResetEventSlim(false);
+            using var item2Written = new ManualResetEventSlim(false);
+            using var connectDone = new ManualResetEventSlim(false);
+
+            var firstDelivery = true;
+
+            // First subscriber: blocks on the first delivery to create the window
+            using var slowSub = cache.Connect().Subscribe(_ =>
+            {
+                if (firstDelivery)
+                {
+                    firstDelivery = false;
+                    delivering.Set();
+
+                    // Wait until item2 has been written and the Connect has subscribed
+                    connectDone.Wait(TimeSpan.FromSeconds(5));
+                }
+            });
+
+            // Write item1 on a background thread — delivery starts, slow subscriber blocks
+            var writeTask = Task.Run(() =>
+            {
+                cache.AddOrUpdate(new TestItem("k1", "v1"));
+            });
+
+            // Wait for delivery of item1 to be in progress (slow sub is blocking)
+            delivering.Wait(TimeSpan.FromSeconds(5)).Should().BeTrue("delivery should have started");
+
+            // Now write item2 on another thread. It will acquire the lock, commit to
+            // ReaderWriter, enqueue a notification, and return. The notification sits
+            // in the queue because the deliverer (Thread A) is blocked by the slow sub.
+            var writeTask2 = Task.Run(() =>
+            {
+                cache.AddOrUpdate(new TestItem("k2", "v2"));
+                item2Written.Set();
+            });
+            item2Written.Wait(TimeSpan.FromSeconds(5)).Should().BeTrue("item2 should have been written");
+
+            // Now Connect on the main thread. The snapshot from ReaderWriter includes
+            // BOTH k1 and k2. The subscription to _changes is added. When the slow
+            // subscriber unblocks, item2's notification will be delivered via OnNext
+            // and the new subscriber will see k2 again — a duplicate Add.
+            var addCounts = new Dictionary<string, int>();
+            using var newSub = cache.Connect().Subscribe(changes =>
+            {
+                foreach (var c in changes)
+                {
+                    if (c.Reason == ChangeReason.Add)
+                    {
+                        var key = c.Current.Key;
+                        addCounts[key] = addCounts.GetValueOrDefault(key) + 1;
+                    }
+                }
+            });
+
+            // Unblock the slow subscriber — delivery resumes, item2 delivered
+            connectDone.Set();
+            writeTask.Wait(TimeSpan.FromSeconds(5)).Should().BeTrue("writeTask should complete");
+            writeTask2.Wait(TimeSpan.FromSeconds(5)).Should().BeTrue("writeTask2 should complete");
+
+            // Each key should appear exactly once in the new subscriber's view
+            addCounts.GetValueOrDefault("k1").Should().Be(1, "k1 should appear once (snapshot only)");
+            addCounts.GetValueOrDefault("k2").Should().Be(1, "k2 should appear once, not duplicated from snapshot + queued delivery");
+        }
+
+        [Fact]
+        public async Task DirectCrossWriteDoesNotDeadlock()
+        {
+            const int iterations = 50;
+
+            for (var iter = 0; iter < iterations; iter++)
+            {
+                using var cacheA = new SourceCache<TestItem, string>(static x => x.Key);
+                using var cacheB = new SourceCache<TestItem, string>(static x => x.Key);
+
+                // Bidirectional: A items flow into B, B items flow into A.
+                // Filter by prefix prevents infinite feedback.
+                using var aToB = cacheA.Connect()
+                    .Filter(static x => x.Key.StartsWith('a'))
+                    .Transform(static (item, _) => new TestItem("from-a-" + item.Key, item.Value))
+                    .PopulateInto(cacheB);
+
+                using var bToA = cacheB.Connect()
+                    .Filter(static x => x.Key.StartsWith('b'))
+                    .Transform(static (item, _) => new TestItem("from-b-" + item.Key, item.Value))
+                    .PopulateInto(cacheA);
+
+                using var barrier = new Barrier(2);
+
+                var taskA = Task.Run(() =>
+                {
+                    barrier.SignalAndWait();
+                    for (var i = 0; i < 1000; i++)
+                    {
+                        cacheA.AddOrUpdate(new TestItem("a" + i, "V" + i));
+                    }
+                });
+
+                var taskB = Task.Run(() =>
+                {
+                    barrier.SignalAndWait();
+                    for (var i = 0; i < 1000; i++)
+                    {
+                        cacheB.AddOrUpdate(new TestItem("b" + i, "V" + i));
+                    }
+                });
+
+                var completed = Task.WhenAll(taskA, taskB);
+                var finished = await Task.WhenAny(completed, Task.Delay(TimeSpan.FromSeconds(60)));
+
+                finished.Should().BeSameAs(completed, $"iteration {iter}: bidirectional cross-cache writes should not deadlock");
+            }
+        }
+
+        [Fact]
+        public async Task MultiCacheFanInDoesNotDeadlock()
+        {
+            const int itemCount = 100;
+
+            using var cacheA = new SourceCache<TestItem, string>(static x => x.Key);
+            using var cacheB = new SourceCache<TestItem, string>(static x => x.Key);
+            using var destination = new SourceCache<TestItem, string>(static x => x.Key);
+            using var subA = cacheA.Connect().PopulateInto(destination);
+            using var subB = cacheB.Connect().PopulateInto(destination);
+            using var results = destination.Connect().AsAggregator();
+
+            var taskA = Task.Run(() =>
+            {
+                for (var i = 0; i < itemCount; i++)
+                {
+                    cacheA.AddOrUpdate(new TestItem($"a-{i}", $"ValueA-{i}"));
+                }
+            });
+
+            var taskB = Task.Run(() =>
+            {
+                for (var i = 0; i < itemCount; i++)
+                {
+                    cacheB.AddOrUpdate(new TestItem($"b-{i}", $"ValueB-{i}"));
+                }
+            });
+
+            var completed = Task.WhenAll(taskA, taskB);
+            var finished = await Task.WhenAny(completed, Task.Delay(TimeSpan.FromSeconds(10)));
+
+            finished.Should().BeSameAs(completed, "concurrent edits with cross-cache subscribers should not deadlock");
+            results.Error.Should().BeNull();
+            results.Data.Count.Should().Be(itemCount * 2, "all items from both caches should arrive in the destination");
+            results.Data.Items.Should().BeEquivalentTo([.. cacheA.Items, .. cacheB.Items], "all items should be in the destination");
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/SourceCacheFixture.UnitTests.cs b/src/DynamicData.Tests/Cache/SourceCacheFixture.UnitTests.cs
new file mode 100644
index 000000000..20bf0772a
--- /dev/null
+++ b/src/DynamicData.Tests/Cache/SourceCacheFixture.UnitTests.cs
@@ -0,0 +1,261 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reactive.Disposables;
+using System.Reactive.Linq;
+
+using FluentAssertions;
+
+using Xunit;
+
+using DynamicData.Tests.Domain;
+using DynamicData.Tests.Utilities;
+
+namespace DynamicData.Tests.Cache;
+
+public static partial class SourceCacheFixture
+{
+    public class UnitTests
+    {
+        [Fact]
+        public void CanHandleABatchOfUpdates()
+        {
+            using var source = new SourceCache<Person, string>(p => p.Key);
+            using var results = source.Connect().AsAggregator();
+
+            source.Edit(
+                updater =>
+                {
+                    var torequery = new Person("Adult1", 44);
+
+                    updater.AddOrUpdate(new Person("Adult1", 40));
+                    updater.AddOrUpdate(new Person("Adult1", 41));
+                    updater.AddOrUpdate(new Person("Adult1", 42));
+                    updater.AddOrUpdate(new Person("Adult1", 43));
+                    updater.Refresh(torequery);
+                    updater.Remove(torequery);
+                    updater.Refresh(torequery);
+                });
+
+            results.Summary.Overall.Count.Should().Be(6, "Should be  6 up`dates");
+            results.Messages.Count.Should().Be(1, "Should be 1 message");
+            results.Messages[0].Adds.Should().Be(1, "Should be 1 update");
+            results.Messages[0].Updates.Should().Be(3, "Should be 3 updates");
+            results.Messages[0].Removes.Should().Be(1, "Should be  1 remove");
+            results.Messages[0].Refreshes.Should().Be(1, "Should be 1 evaluate");
+
+            results.Data.Count.Should().Be(0, "Should be 1 item in` the cache");
+        }
+
+        [Fact]
+        public void ConnectContinuesToWorkNormallyAfterAFailedEdit()
+        {
+            using var source = new SourceCache<int, int>(static item => item);
+    
+            source.AddOrUpdate(1);
+
+            source.Invoking(source => source.Edit(_ => throw new Exception("Test")))
+                .Should().Throw<Exception>()
+                .WithMessage("Test");
+
+            using var subscription = source.Connect().RecordCacheItems(out var results);
+
+            results.Error.Should().BeNull("new subscribers should not receive previous errors");
+            results.RecordedChangeSets.Should().ContainSingle("an initial changeset should have been published.");
+        }
+
+        // Covers https://github.com/reactivemarbles/DynamicData/issues/1129
+        [Fact]
+        public void ConnectDuringEditsDoesNotDuplicate()
+        {
+            using var items = new SourceCache<int, int>(static item => item);
+            
+            using var subscriptions = new CompositeDisposable();
+            
+            // An initial subscription is required to initiate internal buffering of changes, during the upcoming .Edit().
+            // That is, we want there to be changes buffered, internally, when the mid-edit subscription comes in, to
+            // ensure that they don't get duplicated. This is the scenario that came in up #1129. 
+            subscriptions.Add(items
+                .Connect()
+                .Subscribe());
+                
+            CacheItemRecordingObserver<int, int>? results = null;
+                
+            items.Edit(inner =>
+            {
+                inner.AddOrUpdate(1);
+
+                subscriptions.Add(items
+                    .Connect()
+                    .ValidateChangeSets(static item => item)
+                    .RecordCacheItems(out results));
+            
+                results.Error.Should().BeNull("no errors should have occurred");
+                results.RecordedChangeSets.Should().BeEmpty("no changes should be published in the middle of an edit");
+            
+                inner.AddOrUpdate(2);
+
+                results.Error.Should().BeNull("no errors should have occurred");
+                results.RecordedChangeSets.Should().BeEmpty("no changes should be published in the middle of an edit");
+
+                // Explicitly doing a nested edit, as that system is closely intertwined with the edit-tracking system that
+                // .Connect() uses.
+                items.Remove(item: 1);
+
+                results.Error.Should().BeNull("no errors should have occurred");
+                results.RecordedChangeSets.Should().BeEmpty("no changes should be published in the middle of an edit");
+            });
+            
+            results.Should().NotBeNull("the edit delegate should have been invoked");
+            results.Error.Should().BeNull("no errors should have occurred");
+            results.RecordedChangeSets.Should().ContainSingle("subscribers should only receive a single initial changeset");
+            results.RecordedItemsByKey.Should().BeEquivalentTo(
+                new Dictionary<int, int>() { [2] = 2 },
+                options => options.WithoutStrictOrdering(),
+                "all items in the source should have propagated downstream");
+
+            results.HasCompleted.Should().BeFalse("the source has not yet completed");
+        }
+
+        [Fact]
+        public void CountChanged()
+        {
+            using var source = new SourceCache<Person, string>(p => p.Key);
+            using var results = source.Connect().AsAggregator();
+
+            var count = 0;
+            var invoked = 0;
+            using (source.CountChanged.Subscribe(
+                       c =>
+                       {
+                           count = c;
+                           invoked++;
+                       }))
+            {
+                invoked.Should().Be(1);
+                count.Should().Be(0);
+
+                source.AddOrUpdate(new RandomPersonGenerator().Take(100));
+                invoked.Should().Be(2);
+                count.Should().Be(100);
+
+                source.Clear();
+                invoked.Should().Be(3);
+                count.Should().Be(0);
+            }
+        }
+
+        [Fact]
+        public void CountChangedShouldAlwaysInvokeUponSubscription()
+        {
+            using var source = new SourceCache<Person, string>(p => p.Key);
+
+            int? result = null;
+            var subscription = source.CountChanged.Subscribe(count => result = count);
+
+            result.HasValue.Should().BeTrue();
+
+            if (result is null)
+            {
+                throw new InvalidOperationException(nameof(result));
+            }
+
+            result.Value.Should().Be(0, "Count should be zero");
+
+            subscription.Dispose();
+        }
+
+        [Fact]
+        public void CountChangedShouldReflectContentsOfCacheInvokeUponSubscription()
+        {
+            using var source = new SourceCache<Person, string>(p => p.Key);
+
+            var generator = new RandomPersonGenerator();
+            int? result = null;
+            var subscription = source.CountChanged.Subscribe(count => result = count);
+
+            source.AddOrUpdate(generator.Take(100));
+
+            if (result is null)
+            {
+                throw new InvalidOperationException(nameof(result));
+            }
+
+            result.HasValue.Should().BeTrue();
+            result.Value.Should().Be(100, "Count should be 100");
+            subscription.Dispose();
+        }
+
+        [Fact]
+        public void EmptyChanges()
+        {
+            using var source = new SourceCache<Person, string>(p => p.Key);
+
+            IChangeSet<Person, string>? change = null;
+
+            using var subscription = source.Connect(suppressEmptyChangeSets: false)
+                .Subscribe(c=> change = c);
+
+            change.Should().NotBeNull();
+            change!.Count.Should().Be(0);
+        }
+
+        [Fact]
+        public void EmptyChangesWithFilter()
+        {
+            using var source = new SourceCache<Person, string>(p => p.Key);
+
+            IChangeSet<Person, string>? change = null;
+
+            using var subscription = source.Connect(p=>p.Age == 20, suppressEmptyChangeSets: false)
+                .Subscribe(c => change = c);
+
+            change.Should().NotBeNull();
+            change!.Count.Should().Be(0);
+        }
+
+        [Fact]
+        public void StaticFilterRemove()
+        {
+            var cache = new SourceCache<SomeObject, int>(x => x.Id);
+        
+            var above5 = cache.Connect(x => x.Value > 5).AsObservableCache();
+            var below5 = cache.Connect(x => x.Value <= 5).AsObservableCache();
+
+            cache.AddOrUpdate(Enumerable.Range(1,10).Select(i=> new SomeObject(i,i)));
+
+
+            above5.Items.Should().BeEquivalentTo(Enumerable.Range(6, 5).Select(i => new SomeObject(i, i)));
+            below5.Items.Should().BeEquivalentTo(Enumerable.Range(1, 5).Select(i => new SomeObject(i, i)));
+
+            //should move from above 5 to below 5
+            cache.AddOrUpdate(new SomeObject(6,-1));
+
+            above5.Count.Should().Be(4);
+            below5.Count.Should().Be(6);
+
+
+            above5.Items.Should().BeEquivalentTo(Enumerable.Range(7, 4).Select(i => new SomeObject(i, i)));
+            below5.Items.Should().BeEquivalentTo(Enumerable.Range(1, 6).Select(i => new SomeObject(i, i == 6 ? -1 : i)));
+        }
+
+        [Fact]
+        public void SubscribeDisposesCorrectly()
+        {
+            using var source = new SourceCache<Person, string>(p => p.Key);
+
+            var called = false;
+            var errored = false;
+            var completed = false;
+            var subscription = source.Connect().Finally(() => completed = true).Subscribe(updates => { called = true; }, ex => errored = true, () => completed = true);
+            source.AddOrUpdate(new Person("Adult1", 40));
+
+            subscription.Dispose();
+            source.Dispose();
+
+            errored.Should().BeFalse();
+            called.Should().BeTrue();
+            completed.Should().BeTrue();
+        }
+    }
+}
diff --git a/src/DynamicData.Tests/Cache/SourceCacheFixture.cs b/src/DynamicData.Tests/Cache/SourceCacheFixture.cs
index 38fc02e73..ea9de54ed 100644
--- a/src/DynamicData.Tests/Cache/SourceCacheFixture.cs
+++ b/src/DynamicData.Tests/Cache/SourceCacheFixture.cs
@@ -1,426 +1,8 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Reactive.Disposables;
-using System.Reactive.Linq;
-using System.Threading;
-using System.Threading.Tasks;
+namespace DynamicData.Tests.Cache;
 
-using DynamicData.Tests.Domain;
-using DynamicData.Tests.Utilities;
-using FluentAssertions;
-
-using Xunit;
-
-namespace DynamicData.Tests.Cache;
-
-public class SourceCacheFixture : IDisposable
+public static partial class SourceCacheFixture
 {
-    private readonly ChangeSetAggregator<Person, string> _results;
-
-    private readonly ISourceCache<Person, string> _source;
-
-    public SourceCacheFixture()
-    {
-        _source = new SourceCache<Person, string>(p => p.Key);
-        _results = _source.Connect().AsAggregator();
-    }
-
-    [Fact]
-    public void CanHandleABatchOfUpdates()
-    {
-        _source.Edit(
-            updater =>
-            {
-                var torequery = new Person("Adult1", 44);
-
-                updater.AddOrUpdate(new Person("Adult1", 40));
-                updater.AddOrUpdate(new Person("Adult1", 41));
-                updater.AddOrUpdate(new Person("Adult1", 42));
-                updater.AddOrUpdate(new Person("Adult1", 43));
-                updater.Refresh(torequery);
-                updater.Remove(torequery);
-                updater.Refresh(torequery);
-            });
-
-        _results.Summary.Overall.Count.Should().Be(6, "Should be  6 up`dates");
-        _results.Messages.Count.Should().Be(1, "Should be 1 message");
-        _results.Messages[0].Adds.Should().Be(1, "Should be 1 update");
-        _results.Messages[0].Updates.Should().Be(3, "Should be 3 updates");
-        _results.Messages[0].Removes.Should().Be(1, "Should be  1 remove");
-        _results.Messages[0].Refreshes.Should().Be(1, "Should be 1 evaluate");
-
-        _results.Data.Count.Should().Be(0, "Should be 1 item in` the cache");
-    }
-
-    [Fact]
-    public void CountChanged()
-    {
-        var count = 0;
-        var invoked = 0;
-        using (_source.CountChanged.Subscribe(
-                   c =>
-                   {
-                       count = c;
-                       invoked++;
-                   }))
-        {
-            invoked.Should().Be(1);
-            count.Should().Be(0);
-
-            _source.AddOrUpdate(new RandomPersonGenerator().Take(100));
-            invoked.Should().Be(2);
-            count.Should().Be(100);
-
-            _source.Clear();
-            invoked.Should().Be(3);
-            count.Should().Be(0);
-        }
-    }
-
-    [Fact]
-    public void CountChangedShouldAlwaysInvokeUponeSubscription()
-    {
-        int? result = null;
-        var subscription = _source.CountChanged.Subscribe(count => result = count);
-
-        result.HasValue.Should().BeTrue();
-
-        if (result is null)
-        {
-            throw new InvalidOperationException(nameof(result));
-        }
-
-        result.Value.Should().Be(0, "Count should be zero");
-
-        subscription.Dispose();
-    }
-
-    [Fact]
-    public void CountChangedShouldReflectContentsOfCacheInvokeUponSubscription()
-    {
-        var generator = new RandomPersonGenerator();
-        int? result = null;
-        var subscription = _source.CountChanged.Subscribe(count => result = count);
-
-        _source.AddOrUpdate(generator.Take(100));
-
-        if (result is null)
-        {
-            throw new InvalidOperationException(nameof(result));
-        }
-
-        result.HasValue.Should().BeTrue();
-        result.Value.Should().Be(100, "Count should be 100");
-        subscription.Dispose();
-    }
-
-    public void Dispose()
-    {
-        _source.Dispose();
-        _results.Dispose();
-    }
-
-    [Fact]
-    public void SubscribesDisposesCorrectly()
-    {
-        var called = false;
-        var errored = false;
-        var completed = false;
-        var subscription = _source.Connect().Finally(() => completed = true).Subscribe(updates => { called = true; }, ex => errored = true, () => completed = true);
-        _source.AddOrUpdate(new Person("Adult1", 40));
-
-        subscription.Dispose();
-        _source.Dispose();
-
-        errored.Should().BeFalse();
-        called.Should().BeTrue();
-        completed.Should().BeTrue();
-    }
-
-    [Fact]
-    public void EmptyChanges()
-    {
-        IChangeSet<Person, string>? change = null;
-
-        using var subscription = _source.Connect(suppressEmptyChangeSets: false)
-            .Subscribe(c=> change = c);
-
-        change.Should().NotBeNull();
-        change!.Count.Should().Be(0);
-
-    }
-
-    [Fact]
-    public void EmptyChangesWithFilter()
-    {
-        IChangeSet<Person, string>? change = null;
-
-        using var subscription = _source.Connect(p=>p.Age == 20, suppressEmptyChangeSets: false)
-            .Subscribe(c => change = c);
-
-        change.Should().NotBeNull();
-        change!.Count.Should().Be(0);
-    }
-
-    [Fact]
-    public void StaticFilterRemove()
-    {
-        var cache = new SourceCache<SomeObject, int>(x => x.Id);
-        
-        var above5 = cache.Connect(x => x.Value > 5).AsObservableCache();
-        var below5 = cache.Connect(x => x.Value <= 5).AsObservableCache();
-
-        cache.AddOrUpdate(Enumerable.Range(1,10).Select(i=> new SomeObject(i,i)));
-
-
-        above5.Items.Should().BeEquivalentTo(Enumerable.Range(6, 5).Select(i => new SomeObject(i, i)));
-        below5.Items.Should().BeEquivalentTo(Enumerable.Range(1, 5).Select(i => new SomeObject(i, i)));
-
-        //should move from above 5 to below 5
-        cache.AddOrUpdate(new SomeObject(6,-1));
-
-        above5.Count.Should().Be(4);
-        below5.Count.Should().Be(6);
-
-
-        above5.Items.Should().BeEquivalentTo(Enumerable.Range(7, 4).Select(i => new SomeObject(i, i)));
-        below5.Items.Should().BeEquivalentTo(Enumerable.Range(1, 6).Select(i => new SomeObject(i, i == 6 ? -1 : i)));
-    }
-
-    public record class SomeObject(int Id, int Value);
-
-    [Fact]
-    public async Task MultiCacheFanInDoesNotDeadlock()
-    {
-        const int itemCount = 100;
-
-        using var cacheA = new SourceCache<TestItem, string>(static x => x.Key);
-        using var cacheB = new SourceCache<TestItem, string>(static x => x.Key);
-        using var destination = new SourceCache<TestItem, string>(static x => x.Key);
-        using var subA = cacheA.Connect().PopulateInto(destination);
-        using var subB = cacheB.Connect().PopulateInto(destination);
-        using var results = destination.Connect().AsAggregator();
-
-        var taskA = Task.Run(() =>
-        {
-            for (var i = 0; i < itemCount; i++)
-            {
-                cacheA.AddOrUpdate(new TestItem($"a-{i}", $"ValueA-{i}"));
-            }
-        });
-
-        var taskB = Task.Run(() =>
-        {
-            for (var i = 0; i < itemCount; i++)
-            {
-                cacheB.AddOrUpdate(new TestItem($"b-{i}", $"ValueB-{i}"));
-            }
-        });
-
-        var completed = Task.WhenAll(taskA, taskB);
-        var finished = await Task.WhenAny(completed, Task.Delay(TimeSpan.FromSeconds(10)));
-
-        finished.Should().BeSameAs(completed, "concurrent edits with cross-cache subscribers should not deadlock");
-        results.Error.Should().BeNull();
-        results.Data.Count.Should().Be(itemCount * 2, "all items from both caches should arrive in the destination");
-        results.Data.Items.Should().BeEquivalentTo([.. cacheA.Items, .. cacheB.Items], "all items should be in the destination");
-    }
-
-    [Fact]
-    public async Task DirectCrossWriteDoesNotDeadlock()
-    {
-        const int iterations = 50;
-
-        for (var iter = 0; iter < iterations; iter++)
-        {
-            using var cacheA = new SourceCache<TestItem, string>(static x => x.Key);
-            using var cacheB = new SourceCache<TestItem, string>(static x => x.Key);
-
-            // Bidirectional: A items flow into B, B items flow into A.
-            // Filter by prefix prevents infinite feedback.
-            using var aToB = cacheA.Connect()
-                .Filter(static x => x.Key.StartsWith('a'))
-                .Transform(static (item, _) => new TestItem("from-a-" + item.Key, item.Value))
-                .PopulateInto(cacheB);
-
-            using var bToA = cacheB.Connect()
-                .Filter(static x => x.Key.StartsWith('b'))
-                .Transform(static (item, _) => new TestItem("from-b-" + item.Key, item.Value))
-                .PopulateInto(cacheA);
-
-            using var barrier = new Barrier(2);
-
-            var taskA = Task.Run(() =>
-            {
-                barrier.SignalAndWait();
-                for (var i = 0; i < 1000; i++)
-                {
-                    cacheA.AddOrUpdate(new TestItem("a" + i, "V" + i));
-                }
-            });
-
-            var taskB = Task.Run(() =>
-            {
-                barrier.SignalAndWait();
-                for (var i = 0; i < 1000; i++)
-                {
-                    cacheB.AddOrUpdate(new TestItem("b" + i, "V" + i));
-                }
-            });
-
-            var completed = Task.WhenAll(taskA, taskB);
-            var finished = await Task.WhenAny(completed, Task.Delay(TimeSpan.FromSeconds(60)));
-
-            finished.Should().BeSameAs(completed, $"iteration {iter}: bidirectional cross-cache writes should not deadlock");
-        }
-    }
-
-    [Fact]
-    public void ConnectDuringDeliveryDoesNotDuplicate()
-    {
-        // Exploits the dequeue-to-OnNext window. Thread A writes two items in
-        // separate batches. The first delivery is held by a slow subscriber.
-        // While item1 delivery is blocked, item2 is committed to ReaderWriter
-        // and sitting in the queue. Thread B calls Connect(), takes a snapshot
-        // (sees both items), subscribes to _changes, then item2 is delivered
-        // via OnNext — producing a duplicate if not guarded by a generation counter.
-        using var cache = new SourceCache<TestItem, string>(static x => x.Key);
-
-        using var delivering = new ManualResetEventSlim(false);
-        using var item2Written = new ManualResetEventSlim(false);
-        using var connectDone = new ManualResetEventSlim(false);
-
-        var firstDelivery = true;
-
-        // First subscriber: blocks on the first delivery to create the window
-        using var slowSub = cache.Connect().Subscribe(_ =>
-        {
-            if (firstDelivery)
-            {
-                firstDelivery = false;
-                delivering.Set();
-
-                // Wait until item2 has been written and the Connect has subscribed
-                connectDone.Wait(TimeSpan.FromSeconds(5));
-            }
-        });
-
-        // Write item1 on a background thread — delivery starts, slow subscriber blocks
-        var writeTask = Task.Run(() =>
-        {
-            cache.AddOrUpdate(new TestItem("k1", "v1"));
-        });
-
-        // Wait for delivery of item1 to be in progress (slow sub is blocking)
-        delivering.Wait(TimeSpan.FromSeconds(5)).Should().BeTrue("delivery should have started");
-
-        // Now write item2 on another thread. It will acquire the lock, commit to
-        // ReaderWriter, enqueue a notification, and return. The notification sits
-        // in the queue because the deliverer (Thread A) is blocked by the slow sub.
-        var writeTask2 = Task.Run(() =>
-        {
-            cache.AddOrUpdate(new TestItem("k2", "v2"));
-            item2Written.Set();
-        });
-        item2Written.Wait(TimeSpan.FromSeconds(5)).Should().BeTrue("item2 should have been written");
-
-        // Now Connect on the main thread. The snapshot from ReaderWriter includes
-        // BOTH k1 and k2. The subscription to _changes is added. When the slow
-        // subscriber unblocks, item2's notification will be delivered via OnNext
-        // and the new subscriber will see k2 again — a duplicate Add.
-        var addCounts = new Dictionary<string, int>();
-        using var newSub = cache.Connect().Subscribe(changes =>
-        {
-            foreach (var c in changes)
-            {
-                if (c.Reason == ChangeReason.Add)
-                {
-                    var key = c.Current.Key;
-                    addCounts[key] = addCounts.GetValueOrDefault(key) + 1;
-                }
-            }
-        });
-
-        // Unblock the slow subscriber — delivery resumes, item2 delivered
-        connectDone.Set();
-        writeTask.Wait(TimeSpan.FromSeconds(5)).Should().BeTrue("writeTask should complete");
-        writeTask2.Wait(TimeSpan.FromSeconds(5)).Should().BeTrue("writeTask2 should complete");
-
-        // Each key should appear exactly once in the new subscriber's view
-        addCounts.GetValueOrDefault("k1").Should().Be(1, "k1 should appear once (snapshot only)");
-        addCounts.GetValueOrDefault("k2").Should().Be(1, "k2 should appear once, not duplicated from snapshot + queued delivery");
-    }
-
-    // Covers https://github.com/reactivemarbles/DynamicData/issues/1129
-    [Fact]
-    public void ConnectDuringEditsDoesNotDuplicate()
-    {
-        using var items = new SourceCache<int, int>(static item => item);
-        
-        using var subscriptions = new CompositeDisposable();
-        
-        // An initial subscription is required to initiate internal buffering of changes, during the upcoming .Edit().
-        // That is, we want there to be changes buffered, internally, when the mid-edit subscription comes in, to
-        // ensure that they don't get duplicated. This is the scenario that came in up #1129. 
-        subscriptions.Add(items
-            .Connect()
-            .Subscribe());
-            
-        CacheItemRecordingObserver<int, int>? results = null;
-            
-        items.Edit(inner =>
-        {
-            inner.AddOrUpdate(1);
-
-            subscriptions.Add(items
-                .Connect()
-                .ValidateChangeSets(static item => item)
-                .RecordCacheItems(out results));
-        
-            results.Error.Should().BeNull("no errors should have occurred");
-            results.RecordedChangeSets.Should().BeEmpty("no changes should be published in the middle of an edit");
-        
-            inner.AddOrUpdate(2);
-
-            results.Error.Should().BeNull("no errors should have occurred");
-            results.RecordedChangeSets.Should().BeEmpty("no changes should be published in the middle of an edit");
-
-            // Explicitly doing a nested edit, as that system is closely intertwined with the edit-tracking system that
-            // .Connect() uses.
-            items.Remove(item: 1);
-
-            results.Error.Should().BeNull("no errors should have occurred");
-            results.RecordedChangeSets.Should().BeEmpty("no changes should be published in the middle of an edit");
-        });
-        
-        results.Should().NotBeNull("the edit delegate should have been invoked");
-        results.Error.Should().BeNull("no errors should have occurred");
-        results.RecordedChangeSets.Should().ContainSingle("subscribers should only receive a single initial changeset");
-        results.RecordedItemsByKey.Should().BeEquivalentTo(
-            new Dictionary<int, int>() { [2] = 2 },
-            options => options.WithoutStrictOrdering(),
-            "all items in the source should have propagated downstream");
-
-        results.HasCompleted.Should().BeFalse("the source has not yet completed");
-    }
-
-    [Fact]
-    public void ConnectContinuesToWorkNormallyAfterAFailedEdit()
-    {
-        using var source = new SourceCache<int, int>(static item => item);
-    
-        source.AddOrUpdate(1);
-
-        source.Invoking(source => source.Edit(_ => throw new Exception("Test")))
-            .Should().Throw<Exception>()
-            .WithMessage("Test");
-
-        using var subscription = source.Connect().RecordCacheItems(out var results);
-
-        results.Error.Should().BeNull("new subscribers should not receive previous errors");
-        results.RecordedChangeSets.Should().ContainSingle("an initial changeset should have been published.");
-    }
+    public record SomeObject(int Id, int Value);
 
     private sealed record TestItem(string Key, string Value);
 }