From 7ebcfb5268e0c91b58c5024ae48cd661fba47a05 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 10 Sep 2026 19:43:15 +0000
Subject: [PATCH 1/4] Initial plan


From 8d11bf9b0f7b2ac7b6072c4aa82eae16530cd1cb Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 10 Sep 2026 19:46:00 +0000
Subject: [PATCH 2/4] Document DoNotParallelize deferral and cancellation
 behavior

Co-authored-by: meaghanlewis <10103121+meaghanlewis@users.noreply.github.com>
---
 ...it-testing-mstest-writing-tests-controlling-execution.md | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md b/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md
index f030eb959b62d..244a924110810 100644
--- a/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md
+++ b/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md
@@ -152,6 +152,10 @@ The `Workers` property specifies the maximum number of threads for parallel exec
 
 The <xref:Microsoft.VisualStudio.TestTools.UnitTesting.DoNotParallelizeAttribute> prevents parallel execution for specific assemblies, classes, or methods. Use this attribute when tests share state or resources that can't be safely accessed concurrently.
 
+When you enable in-assembly parallelization, MSTest partitions each test source (assembly) into parallelizable and nonparallelizable tests. MSTest runs the parallelizable set first, then runs the `DoNotParallelize` set one test at a time at the end of that source's run. In runs that include multiple test sources, each source has its own deferred tail. Because deferred tests can't overlap with other tests, a slow deferred test usually increases total run time by about its own duration.
+
+Because MSTest runs deferred tests only after the parallelizable phase finishes, a canceled or aborted run can end before MSTest executes deferred tests.
+
 ```csharp
 [assembly: Parallelize(Scope = ExecutionScope.MethodLevel)]
 
@@ -195,7 +199,7 @@ public class MixedTests
 ```
 
 > [!NOTE]
-> You only need `DoNotParallelize` when you've enabled parallel execution with the `Parallelize` attribute.
+> You only need `DoNotParallelize` when you've enabled parallel execution with the `Parallelize` attribute. When parallelization is disabled (the default), `DoNotParallelize` has no effect.
 
 ### `ResourceLockAttribute`
 

From e08d5c15f8fd114fdde8683fc2794b2abe793aac Mon Sep 17 00:00:00 2001
From: "Meaghan Osagie (Lewis)" <mosagie@microsoft.com>
Date: Fri, 11 Sep 2026 16:32:13 -0700
Subject: [PATCH 3/4] Update documentation on MSTest deferred test execution

Clarify that the execution order of deferred tests is an internal detail and may change in future MSTest versions.
---
 .../unit-testing-mstest-writing-tests-controlling-execution.md  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md b/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md
index 244a924110810..78c262ee6fb9c 100644
--- a/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md
+++ b/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md
@@ -154,7 +154,7 @@ The <xref:Microsoft.VisualStudio.TestTools.UnitTesting.DoNotParallelizeAttribute
 
 When you enable in-assembly parallelization, MSTest partitions each test source (assembly) into parallelizable and nonparallelizable tests. MSTest runs the parallelizable set first, then runs the `DoNotParallelize` set one test at a time at the end of that source's run. In runs that include multiple test sources, each source has its own deferred tail. Because deferred tests can't overlap with other tests, a slow deferred test usually increases total run time by about its own duration.
 
-Because MSTest runs deferred tests only after the parallelizable phase finishes, a canceled or aborted run can end before MSTest executes deferred tests.
+Because MSTest runs deferred tests only after the parallelizable phase finishes, a canceled or aborted run can end before MSTest executes deferred tests. The execution order described here is an internal implementation detail and isn't a public contract. It might change in a future version of MSTest. 
 
 ```csharp
 [assembly: Parallelize(Scope = ExecutionScope.MethodLevel)]

From d601e128205dea4482f1de026544969afcedb07f Mon Sep 17 00:00:00 2001
From: "Meaghan Osagie (Lewis)" <mosagie@microsoft.com>
Date: Fri, 11 Sep 2026 16:34:59 -0700
Subject: [PATCH 4/4] Fix formatting issue in MSTest documentation

---
 .../unit-testing-mstest-writing-tests-controlling-execution.md  | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md b/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md
index 78c262ee6fb9c..741301193eb75 100644
--- a/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md
+++ b/docs/core/testing/unit-testing-mstest-writing-tests-controlling-execution.md
@@ -154,7 +154,7 @@ The <xref:Microsoft.VisualStudio.TestTools.UnitTesting.DoNotParallelizeAttribute
 
 When you enable in-assembly parallelization, MSTest partitions each test source (assembly) into parallelizable and nonparallelizable tests. MSTest runs the parallelizable set first, then runs the `DoNotParallelize` set one test at a time at the end of that source's run. In runs that include multiple test sources, each source has its own deferred tail. Because deferred tests can't overlap with other tests, a slow deferred test usually increases total run time by about its own duration.
 
-Because MSTest runs deferred tests only after the parallelizable phase finishes, a canceled or aborted run can end before MSTest executes deferred tests. The execution order described here is an internal implementation detail and isn't a public contract. It might change in a future version of MSTest. 
+Because MSTest runs deferred tests only after the parallelizable phase finishes, a canceled or aborted run can end before MSTest executes deferred tests. The execution order described here is an internal implementation detail and isn't a public contract. It might change in a future version of MSTest.
 
 ```csharp
 [assembly: Parallelize(Scope = ExecutionScope.MethodLevel)]