Fix DisableAppDomain default value when not running in isolation under VSTest

[Copilot]

Plan for adding VSTest console integration tests for AppDomain scenario:

• Extract vstest.console.exe locator helper from CLITestBase.e2e.cs to a shared VSTestConsoleLocator class
• Update CLITestBase.e2e.cs to use the new shared VSTestConsoleLocator class
• Update MSTest.Acceptance.IntegrationTests project to reference the VSTestConsoleLocator
• Expand AppDomainTests.cs to include tests that use vstest.console.exe directly
• Fix CommandLine usage with proper command line formatting
• Improve error messages to include stderr for better diagnostics
• Refactor to reduce code duplication with helper methods
• Add null check in GetTestPlatformVersion to prevent null reference exceptions
• Fix nullable reference warnings for environment variables
• Fix formatting issues (remove trailing whitespace)
• Remove unnecessary package reference
• Address code review feedback
• Build and test the changes (blocked by network issues, will be tested in CI)

Summary

This PR addresses the issue where AppDomain should be enabled by default when running VSTest. The changes include:

1. Created VSTestConsoleLocator class (test/Utilities/Automation.CLI/VSTestConsoleLocator.cs):

   • Extracted the vstest.console.exe location logic from CLITestBase.e2e.cs
   • Made it reusable across different test projects
   • Provides a static method GetConsoleRunnerPath() to locate vstest.console.exe
   • Includes proper null checks and handles nullable environment variables correctly

2. Updated CLITestBase.e2e.cs:

   • Removed duplicate vstest.console.exe locator code
   • Now uses the shared VSTestConsoleLocator class

3. Expanded AppDomainTests.cs:

   • Added two new test methods: RunTests_With_VSTestConsole_Directly and DiscoverTests_With_VSTestConsole_Directly
   • These tests run vstest.console.exe directly (not through dotnet test)
   • Tests validate AppDomain behavior with different DisableAppDomain settings (true, false, null)
   • Tests build the test project, locate the DLL, and run vstest.console.exe with optional runsettings
   • Added helper methods to reduce code duplication

4. Updated MSTest.Acceptance.IntegrationTests.csproj:

   • Added link to VSTestConsoleLocator.cs for shared access

The new tests will expose any issues with AppDomain configuration when running under vstest.console.exe directly (as opposed to testhost.exe), which was the original problem described in the issue.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Appdomain should be enabled by default when running VSTest</issue_title>
<issue_description>

testfx/src/Adapter/MSTestAdapter.PlatformServices/Services/MSTestAdapterSettings.cs

Lines 190 to 199 in 8b43ebb

	// HACK: When running VSTest, and VSTest didn't create TestHostAppDomain (default behavior), we must be enabling appdomain in MSTest.
	// Otherwise, we will not merge app.config properly, nor we will have correct BaseDirectory of current domain.
	#if NETFRAMEWORK
	if (AppDomain.CurrentDomain.Id == 1 &&
	AppDomain.CurrentDomain.FriendlyName.StartsWith("testhost.", StringComparison.Ordinal) &&
	AppDomain.CurrentDomain.FriendlyName.EndsWith(".exe", StringComparison.Ordinal))
	{
	disableAppDomain = false;
	}
	#endif

This hack to enable appdomain by default in VSTest isn't enough. It only works when running in isolation (i.e, under testhost.exe). However, if we run under vstest.console directly, we don't get the expected behavior.</issue_description>

<agent_instructions>Write an acceptance integration test for this scenario. The scenario must use vstest.console.exe directly instead of dotnet test.

Note: There are already tests in test/IntegrationTests/MSTest.Acceptance.IntegrationTests/AppDomainTests.cs. They should only be expanded to run with both dotnet test and also with vstest.console.exe directly.

Also note that test/Utilities/Automation.CLI/CLITestBase.e2e.cs already contains a helper to locate vstest.console.exe. Consider extracting the helper to a VSTestConsoleLocator helper class that is shared in the two projects.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Appdomain should be enabled by default when running VSTest #6894

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[Youssef1313]

@copilot

test/Utilities/Automation.CLI/VSTestConsoleLocator.cs(46,42): error CS8600: (NETCORE_ENGINEERING_TELEMETRY=Build) Converting null literal or possible null value to non-nullable type.

[Copilot]

@copilot

test/Utilities/Automation.CLI/VSTestConsoleLocator.cs(46,42): error CS8600: (NETCORE_ENGINEERING_TELEMETRY=Build) Converting null literal or possible null value to non-nullable type.
...

Fixed in 327f5c9. Changed string to string? for environment variable return values and added a null check for USERPROFILE with a descriptive exception message.

[Youssef1313]

test/IntegrationTests/MSTest.Acceptance.IntegrationTests/AppDomainTests.cs(173,1): error IDE0055: (NETCORE_ENGINEERING_TELEMETRY=Build) Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055)

@copilot

[Copilot]

test/IntegrationTests/MSTest.Acceptance.IntegrationTests/AppDomainTests.cs(173,1): error IDE0055: (NETCORE_ENGINEERING_TELEMETRY=Build) Fix formatting (https://learn.microsoft.com/dotnet/fundamental...

Fixed in 19a8212. Removed trailing whitespace on lines 173 and 221.

[Youssef1313]

/backport to rel/4.0

[github-actions]

Started backporting to rel/4.0: https://github.com/microsoft/testfx/actions/runs/19171676553