Process tests do not return for 5 minutes

[danmoseley]

If you run the System.Diagnostics.Process tests locally on Windows, after the tests themselves complete there will be a 5 minute delay before dotnet build /t:test returns. this happens after this point:

  === TEST EXECUTION SUMMARY ===
     System.Diagnostics.Process.Tests  Total: 302, Errors: 0, Failed: 0, Skipped: 1, Time: 52.678s
  ----- end Wed 11/11/2020 10:12:30.44 ----- exit code 0 ----------------------------------------------------------

This is because MSBuild is waiting on the spawned cmd process that runs xunit, and that is waiting on two test processes that the tests created but did not terminate. Both of those were clearly created with CreateProcessLong() because they are doing a 5 minute sleep. Such processes are intended to be terminated by tests. It needs to be figured out which test isn't terminating them. I looked through the code and didn't see the issue; bisection may help.

After fixing that, there is another delay, this one in the WaitAsyncForProcess() test: it creates a process that sleeps for 30 seconds, and waits for it to exit. Probably instead the child process should wait to exit on some event set by the parent after the parent has called WaitForExitAsync(). Note this test is outerloop.

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Issue meta data

Issue content:	If you run the System.Diagnostics.Process tests locally on Windows, after the tests themselves complete there will be a 5 minute delay before `dotnet build /t:test` returns. this happens after this point: ``` === TEST EXECUTION SUMMARY === System.Diagnostics.Process.Tests Total: 302, Errors: 0, Failed: 0, Skipped: 1, Time: 52.678s ----- end Wed 11/11/2020 10:12:30.44 ----- exit code 0 ---------------------------------------------------------- ``` This is because MSBuild is waiting on the spawned cmd process that runs xunit, and that is waiting on two test processes that the tests created but did not terminate. Both of those were clearly reated with `CreateProcessLong()` because they are doing a 5 minute sleep. Such processes are intended to be terminated by tests. It needs to be figured out which test isn't terminating them. After fixing that, there is another delay, this one in the WaitAsyncForProcess() test: it creates a process that sleeps for 30 seconds, and waits for it to exit. Probably instead the child process should wait to exit on some event set by the parent after the parent has called WaitForExitAsync(). Note this test is outerloop.
Issue author:	danmosemsft
Assignees:	-
Milestone:	-

[danmoseley]

Noted in #44392. This isn't an urgent issue, but it presumably ties up the test machines for 5 minutes longer than necessary.