[Jakub Jareš (nohwnd)]

An ITestExecutor2 that can't be instantiated (for example one without a parameterless constructor) throws while merging the ITestExecutor and ITestExecutor2 lists in MergeTestExtensionLists. That throw tears down the whole executor extension manager: GetExecutorExtensionManager catches it and returns null for the entire assembly, so every executor in that assembly — including the real one — becomes unreachable. The run ends with Could not find test executor 'executor://mstestadapter/v2' and 0 tests run. Discovery survives because it doesn't force instantiation.

The fix skips the one bad executor instead of failing the whole merge, and applies the same per-item resilience to the other loops that eagerly instantiate extensions:

• MergeTestExtensionLists — the root cause. Wrap .Value per extension and keep the already-cached good version on failure.
• LoadAndInitializeAllExtensions for executors, discoverers, and settings providers — move the try/catch inside the loop so one bad extension doesn't stop the rest. It still rethrows when the caller asked to fail on error.
• BaseRunTests debugger-attach loop — a rogue .Value there no longer aborts before the already-resilient execution loop.

The regression test lives in TestExecutorExtensionManagerTests, with a good and a rogue ITestExecutor2 hosted in TestUtilities so it stays isolated from the tests that assert every discovered executor is created. It throws MissingMethodException without the merge fix and passes with it.

[Copilot]

Pull request overview

This PR hardens vstest’s extension loading so that a single misconfigured/broken extension (e.g., an ITestExecutor2 without a parameterless constructor) doesn’t prevent other valid extensions in the same assembly from being discovered and used. This improves reliability of adapter/executor discovery and execution in the presence of “rogue” extensions.

Changes:

• Make TestExecutorExtensionManager.MergeTestExtensionLists resilient by handling instantiation failures per extension and continuing the merge.
• Move try/catch inside “eager instantiation” loops for executors, discoverers, and settings providers so one failing extension doesn’t block the rest (unless the caller opts into failing).
• Prevent a rogue executor from aborting the debugger-attach pre-pass in BaseRunTests, allowing remaining executors to proceed.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/Microsoft.TestPlatform.TestUtilities/ResilientExecutorFixtures.cs	Adds a “good” and “rogue” ITestExecutor2 fixture to reproduce instantiation failures in a controlled assembly.
test/Microsoft.TestPlatform.Common.UnitTests/ExtensionFramework/TestExecutorExtensionManagerTests.cs	Adds a regression test ensuring executor extension manager creation remains resilient and keeps good executors discoverable.
src/Microsoft.TestPlatform.CrossPlatEngine/Execution/BaseRunTests.cs	Wraps debugger-attach condition evaluation to avoid aborting the run when an executor instantiation fails early.
src/Microsoft.TestPlatform.Common/SettingsProvider/SettingsProviderExtensionManager.cs	Adjusts Load/Initialize behavior to be per-provider resilient, optionally failing when requested.
src/Microsoft.TestPlatform.Common/ExtensionFramework/TestExecutorExtensionManager.cs	Adds per-extension resilience to merge and eager loading paths to avoid whole-manager failure.
src/Microsoft.TestPlatform.Common/ExtensionFramework/TestDiscoveryExtensionManager.cs	Makes discoverer initialization resilient per discoverer, while preserving fail-fast when requested.