[v5] Remove VSTest support from the test adapter and make MTP the default

[Evangelink]

Summary

First slice of the v5 work to run MSTest exclusively on Microsoft.Testing.Platform (MTP). Targets the long-lived dev/v5 branch (created from main).

This PR removes the VSTest reflection surface (ITestExecutor/ITestDiscoverer and friends) from MSTest.TestAdapter and makes MTP the only engine by removing the EnableMSTestRunner opt-in. MSTest now runs solely in MTP mode.

Crucially, this does not mean MSTest stops working under vstest.console. Starting with VSTest 18.10, VSTest knows how to host an MTP test host under VSTest, so an MTP-only test app (like MSTest v5) is still runnable through vstest.console — it just runs as an MTP app (MTP extensions are not surfaced in that hosting mode). This PR bumps VSTest to 18.10.0-preview-26357-05 so that path works, which is what keeps the VSTest-based tests green.

Changes

• buildTransitive/common/MSTest.TestAdapter.targets — remove the EnableMSTestRunner opt-in / VSTest coexistence branch; the adapter is now always a testing platform application (IsTestingPlatformApplication=true, GenerateProgramFile=false). Adds a transitional MSTest_WarnOnObsoleteEnableMSTestRunner warning when a leftover EnableMSTestRunner value is detected (suppressible via SuppressMSTestRunnerObsoleteWarning).
• Properties/AssemblyInfo.cs — drop [assembly: TestExtensionTypes(typeof(MSTestDiscoverer), typeof(MSTestExecutor))] (the VSTest extension registration).
• EqtTraceLogger.cs — deleted. PlatformServiceProvider.AdapterTraceLogger defaults to NopTraceLogger, and MTP installs MTPTraceLogger, so no bootstrap is needed.
• MSTestExecutor.cs — remove ITestExecutor, [ExtensionUri], the parameterless ctor, the EqtTrace bootstrap, the public RunTests(...) overloads, and the now-dead TestCase-based RunTestsAsync overload + ToUnitTestElement (MTP always runs from sources). The internal source-based execution engine used by MSTestBridgedTestFramework is untouched.
• MSTestDiscoverer.cs — remove ITestDiscoverer, [FileExtension]/[DefaultExecutorUri], the parameterless ctor, and the public DiscoverTests(...) entry point. The internal discovery engine used by the MTP bridge is untouched.
• Folder consolidation — delete the VSTestAdapter/ and TestingPlatformAdapter/ folders and move all their files (the shared MSTestExecutor/MSTestDiscoverer engine + the MTP extension files) to the MSTest.TestAdapter project root. Namespaces unchanged.
• Directory.Packages.props — bump VSTest (MicrosoftNETTestSdkVersion and Microsoft.TestPlatform.Filter.Source) to 18.10.0-preview-26357-05 so VSTest can host the MTP test host.
• MSTestAdapter.UnitTests — the removed VSTest reflection surface broke these tests: deleted the tests asserting on removed VSTest attributes and rewrote the behavioral tests to drive the internal MTP engine (DiscoverTestsAsync / RunTestsAsync(sources, ...)).
• FrameworkHandlerAdapter.cs (VSTestBridge) — IFrameworkHandle.EnableShutdownAfterTestRun became [Obsolete] ("has no effect") in the new object model; suppress CS0618 while keeping the interface implementation and historical pass-through.

Why this is only a first slice

The MTP path still consumes the VSTest object model through Microsoft.Testing.Extensions.VSTestBridge (VSTestRunTestExecutionRequest, IFrameworkHandle, TestCase, …). Fully decoupling from the object model is a separate, larger effort the codebase already flags as a long-term goal ("the eventual goal should be to stop using the VSTestBridge altogether").

Verification

Full repo builds cleanly (0 errors), including all MSTest.TestAdapter TFMs (net462, net8.0, net9.0, UWP, WinUI). The rewritten MSTestAdapter.UnitTests classes pass (12 tests).

Follow-ups (subsequent PRs on dev/v5)

• Remove EnableMSTestRunner / VSTest coexistence from Microsoft.Testing.Platform.MSBuild.targets and every other reference.
• MSTest.Sdk: remove UseVSTest and Sdk/VSTest/; make the Runner the only engine.
• Remove the VSTestBridge object-model coupling from the adapter (neutral request model).
• Drop the isMTP flag that threads through MSTestExecutor → TestExecutionManager → UnitTestDiscoverer → AssemblyEnumeratorWrapper (always true now); requires updating the kept MSTestAdapter.PlatformServices.UnitTests call sites.
• Update samples and docs; remove EnableMSTestRunner from all .csproj.
• Update --help/--info acceptance expectations if any option surface changes.

[Copilot]

Pull request overview

This is the first slice of the v5 effort to drop full VSTest support from MSTest.TestAdapter and run MSTest exclusively on Microsoft.Testing.Platform (MTP). It removes the VSTest reflection surface (ITestExecutor/ITestDiscoverer implementations, extension-registration attributes, parameterless constructors, and public entry points) and the EnableMSTestRunner opt-in, making the adapter always a testing-platform application. The internal execution/discovery engine consumed by MSTestBridgedTestFramework is left intact, and the change verified that the src project still builds across all TFMs. It targets the long-lived dev/v5 branch and is deliberately a draft: VSTest-specific test projects are knowingly left broken for follow-up PRs.

Changes:

• Strip VSTest coupling from MSTestExecutor/MSTestDiscoverer (interfaces, [ExtensionUri]/[FileExtension]/[DefaultExecutorUri], parameterless ctors, public RunTests/DiscoverTests) and drop the EqtTrace bootstrap plus the EqtTraceLogger file.
• Remove the [assembly: TestExtensionTypes(...)] VSTest extension registration.
• Simplify MSTest.TestAdapter.targets to always set IsTestingPlatformApplication=true and GenerateProgramFile=false, removing the EnableMSTestRunner coexistence branch.

Show a summary per file

File	Description
src/Adapter/MSTest.TestAdapter/VSTestAdapter/MSTestExecutor.cs	Drops ITestExecutor, [ExtensionUri], parameterless ctor, EqtTrace bootstrap, and public RunTests overloads; keeps internal engine used by the MTP bridge.
src/Adapter/MSTest.TestAdapter/VSTestAdapter/MSTestDiscoverer.cs	Drops ITestDiscoverer, file-extension/executor-uri attributes, parameterless ctor, and public DiscoverTests; keeps internal discovery path.
src/Adapter/MSTest.TestAdapter/VSTestAdapter/EqtTraceLogger.cs	Deleted; default NopTraceLogger + MTP's MTPTraceLogger cover logging.
src/Adapter/MSTest.TestAdapter/Properties/AssemblyInfo.cs	Removes VSTest extension-type registration (also inadvertently drops the file's UTF-8 BOM — flagged).
src/Adapter/MSTest.TestAdapter/buildTransitive/common/MSTest.TestAdapter.targets	Removes EnableMSTestRunner opt-in; adapter is now unconditionally an MTP application.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Medium

[github-actions]

Note

🤖 Automated review by GitHub Copilot. Generated by the Expert Code Review workflow. To request a follow-up action, reply by tagging @copilot directly.

#	Dimension	Verdict
20	Build Infrastructure & Dependencies	🟡 1 MODERATE (suggestion for follow-up)

✅ 21/22 dimensions clean.

• Build Infrastructure — users with EnableMSTestRunner=false silently get MTP on v5 upgrade (tracked for follow-up)

Dimension notes:

• 1–3 (Correctness, Threading, Security): Clean. EqtTraceLogger removal is safe — PlatformServiceProvider.AdapterTraceLogger defaults to NopTraceLogger.Instance and MSTestBridgedTestFramework ctor sets MTPTraceLogger before any execution/discovery call. No new shared state or threading concerns.
• 4 (Public API): No breaking change — MSTestDiscoverer and MSTestExecutor were already internal sealed. The public members existed only to satisfy the VSTest interface contracts.
• 5–9 (Performance, Cross-TFM, Resources, Defensive Coding, Localization): N/A or clean. Module initializer does less work now (perf improvement).
• 10–14 (Test dimensions): N/A — no test files changed. Acknowledged that CI is expected to be red until follow-up test project updates land.
• 15–17 (Structure, Naming, Docs): Clean. Minor note: // TODO: Verify why VSTest annotates the IEnumerable as nullable. at MSTestExecutor.cs:77 is now stale (VSTest no longer calls this path) and lacks an issue reference per repo policy — can be cleaned up when the isMTP flag removal follow-up lands.
• 18–19 (Analyzer, IPC): N/A.
• 20 (Build Infrastructure): See inline comment on .targets file — suggestion for migration warning in follow-up.
• 21 (Scope & PR Discipline): Well-scoped first slice. Follow-ups are enumerated clearly. Consider tracking them as GitHub issues for discoverability.
• 22 (PowerShell): N/A.

MSBuild Authoring (supplemental): The .targets change follows correct MSBuild patterns — Condition=" '$(Prop)' == '' " for safe defaults in a transitive targets file. No anti-patterns detected.

[github-actions]

🧪 Test quality grade — PR #9726

Grade	Test	Notes
B (80–89)	mod UseCooperativeCancellationForTimeoutAnalyzerTests. WhenTimeoutAttributeWithoutCooperativeCancellation_ CodeFixOffersTaskRunTestMethod	Strong assertion: verifies both diagnostic location and transformed code; body is mildly long due to raw string literals — consider extracting expected snippets to named local variables for readability.
A (90–100)	mod UseCooperativeCancellationForTimeoutAnalyzerTests. WhenTaskRunTestMethodAttributeWithTimeout_ NoDiagnostic	No issues found. Note: orphaned stray lines after the closing brace in the raw diff may indicate a copy-paste artifact that could break compilation.

_{This advisory comment was generated automatically. Grades are heuristic
and informational — they do not block merging. Re-run with
/grade-tests.}

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🤖 Automated content by GitHub Copilot. Generated by the Grade Tests on PR (on open / sync) workflow. · 80.5 AIC · ⌖ 3.99 AIC · ⊞ 8.9K · [◷]( · ◷)