Fix failing performance test

src/SIL.Harmony.Sample/CrdtSampleKernel.cs

@@ -22,7 +22,8 @@ public static IServiceCollection AddCrdtDataSample(this IServiceCollection servi
         {
             //this ensures that Ef Conversion methods will not be cached across different IoC containers
             //this can show up as the second instance using the JsonSerializerOptions from the first container
-            //only needed for testing scenarios
+            //But, for testing scenarios (performanceTest: true) this essentially restores EF Core's default service-provider caching
+            //(which is otherwise disabled for test isolation) and thus matches real ASP.NET Core app config
             builder.EnableServiceProviderCaching(performanceTest);
             builder.UseLinqToDbCrdt(provider);
             optionsBuilder(builder);

src/SIL.Harmony.Tests/DataModelPerformanceTests.cs

@@ -78,7 +78,7 @@ private static async Task<TimeSpan> MeasureTime(Func<Task> action, int iteration
     public async Task SimpleAddChangePerformanceTest()
     {
         //disable validation because it's slow
-        var dataModelTest = new DataModelTestBase(alwaysValidate: false);
+        var dataModelTest = new DataModelTestBase(alwaysValidate: false, performanceTest: true);
         // warmup the code, this causes jit to run and keeps our actual test below consistent
         await dataModelTest.WriteNextChange(dataModelTest.SetWord(Guid.NewGuid(), "entity 0"));
         var runtimeAddChange1Snapshot = await MeasureTime(() => dataModelTest.WriteNextChange(dataModelTest.SetWord(Guid.NewGuid(), "entity 1")).AsTask());
@@ -87,6 +87,9 @@ public async Task SimpleAddChangePerformanceTest()
         //fork the database, this creates a new DbContext which does not have a cache of all the snapshots created above
         //that cache causes DetectChanges (used by SaveChanges) to be slower than it should be
         dataModelTest = dataModelTest.ForkDatabase(false);
+        //warmup the forked context too — it has a fresh ServiceProvider/DbContext/DataModel,
+        //so the first WriteNextChange pays EF Core query-compilation cost that the measurement shouldn't include
+        await dataModelTest.WriteNextChange(dataModelTest.SetWord(Guid.NewGuid(), "entity warmup"));
 
         await StartTrace();
         var runtimeAddChange10000Snapshots = await MeasureTime(() => dataModelTest.WriteNextChange(dataModelTest.SetWord(Guid.NewGuid(), "entity1")).AsTask());