Extract duplicate STA thread dispatch pattern into StaThreadHelper

[Copilot]

The same ~40-line STA thread dispatch block (check → create named thread → set STA → start → join → warn on non-Windows) was copy-pasted in TestClassInfo.Initializer.cs and TestClassInfo.Cleanup.cs, making any bug fix or behavioral change require parallel edits.

Changes

• New StaThreadHelper.RunOnStaThreadIfNeededAsync<TResult> in MSTestAdapter.PlatformServices/Helpers/ — generic helper encapsulating the full STA dispatch pattern:

  • Checks needsSta && Windows && currentThread != STA
  • Creates a named STA thread, starts it, joins it
  • Catches only ThreadStateException | ThreadInterruptedException from Join() (the only types documented to be thrown), logs with thread name context, returns defaultResult
  • Logs the non-Windows STA warning when applicable
  • Falls back to direct await otherwise

• TestClassInfo.Initializer.cs and TestClassInfo.Cleanup.cs — ~80 lines of duplicated dispatch replaced with 4–5 line call sites each:

// Before: ~40 lines of inline STA thread setup
bool isSTATestClass = ClassAttribute is STATestClassAttribute;
bool isWindowsOS = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
if (isSTATestClass && isWindowsOS && Thread.CurrentThread.GetApartmentState() != ApartmentState.STA)
{
    TestResult? result = null;
    var entryPointThread = new Thread(() => result = DoRunAsync().GetAwaiter().GetResult())
    { Name = "MSTest STATestClass ClassCleanup" };
    entryPointThread.SetApartmentState(ApartmentState.STA);
    entryPointThread.Start();
    try { entryPointThread.Join(); }
    catch (Exception ex) { /* log */ }
    return result;
}
else
{
    if (!isWindowsOS && isSTATestClass) { /* warn */ }
    return await DoRunAsync().ConfigureAwait(false);
}

// After: 4 lines
return await StaThreadHelper.RunOnStaThreadIfNeededAsync(
    needsSta: ClassAttribute is STATestClassAttribute,
    action: DoRunAsync,
    threadName: "MSTest STATestClass ClassCleanup",
    defaultResult: null).ConfigureAwait(false);

TestExecutionManager.DefaultFactoryAsync and MSTestExecutor.RunTestsFromRightContextAsync are out of scope — both use structurally different mechanisms (TCS-based exception bridging and Task.Run(Join, cancellationToken) respectively) that don't fit this abstraction.

[Copilot]

Pull request overview

This PR reduces duplication in the MSTest adapter’s STA dispatch logic by centralizing the “run on a dedicated STA thread when required” pattern into a single helper, and updating ClassInitialize/ClassCleanup to use it.

Changes:

• Added StaThreadHelper.RunOnStaThreadIfNeededAsync<TResult> to encapsulate STA thread creation, start, join, and non-Windows warning behavior.
• Replaced duplicated STA dispatch blocks in TestClassInfo.Initializer.cs and TestClassInfo.Cleanup.cs with a single helper call each.
• Standardized Join() exception handling/logging in the extracted helper.

Show a summary per file

File	Description
src/Adapter/MSTestAdapter.PlatformServices/Helpers/StaThreadHelper.cs	Introduces a reusable STA-thread dispatch helper used by adapter execution paths.
src/Adapter/MSTestAdapter.PlatformServices/Execution/TestClassInfo.Initializer.cs	Uses the helper for ClassInitialize STA dispatch, removing duplicated thread/join logic.
src/Adapter/MSTestAdapter.PlatformServices/Execution/TestClassInfo.Cleanup.cs	Uses the helper for ClassCleanup STA dispatch, removing duplicated thread/join logic.

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 2