`dotnet test` for MTP throws hard-to-interpret KeyNotFoundException

[Youssef1313]

So far I saw it only once, but I think it's worth investigating:

The following exception occurred when running the test module with RunCommand '/Users/runner/work/1/s/artifacts/bin/Microsoft.Testing.Extensions.UnitTests/Debug/net9.0/Microsoft.Testing.Extensions.UnitTests' and RunArguments '  --diagnostic --diagnostic-output-directory /Users/runner/work/1/s/artifacts/log/Debug --diagnostic-file-prefix Microsoft.Testing.Extensions.UnitTests_net9.0_Debug_x64 --diagnostic-verbosity trace --crashdump --hangdump --hangdump-timeout 15m --report-azdo --coverage --coverage-settings /Users/runner/work/1/s/test/coverage.config --coverage-output Microsoft.Testing.Extensions.UnitTests_net9.0_Debug_x64.coverage --report-trx --report-trx-filename Microsoft.Testing.Extensions.UnitTests_net9.0_x64.trx --results-directory /Users/runner/work/1/s/artifacts/TestResults/Debug/':

System.Collections.Generic.KeyNotFoundException: The given key 'ba98a3b7d1b0470a866ea837070091b8' was not present in the dictionary.
   at System.Collections.Concurrent.ConcurrentDictionary`2.ThrowKeyNotFoundException(TKey key)
   at System.Collections.Concurrent.ConcurrentDictionary`2.get_Item(TKey key)
   at Microsoft.DotNet.Cli.Commands.Test.Terminal.TerminalTestReporter.AssemblyRunCompleted(String executionId, Int32 exitCode, String outputData, String errorData)
   at Microsoft.DotNet.Cli.Commands.Test.TestApplicationHandler.OnTestProcessExited(Int32 exitCode, String outputData, String errorData)
   at Microsoft.DotNet.Cli.Commands.Test.TestApplication.RunAsync()
   at Microsoft.DotNet.Cli.Commands.Test.TestApplication.RunAsync()
   at Microsoft.DotNet.Cli.Commands.Test.TestApplicationActionQueue.Read(BuildOptions buildOptions, TestOptions testOptions, TerminalTestReporter output, Action`1 onHelpRequested)

In addition, this exception was just buried somewhere in the middle of the output and wasn't surfaced towards the end of the output.

[Youssef1313]

I have a theory here.

We started a test host controller, the test host controller failed for some reason and exited. In that case, we got a handshake from the controller, but we never called AssemblyRunStarted because the testhost didn't start. Then we called AssemblyRunCompleted, but the key won't be found in the dictionary.

What is missing here:

• Are we burying the reason why test host controller failed?
• The error should probably surface in a better way.
• The error should be re-printed towards the end.