Python process exiting abruptly on windows-2019

[jlaine]

I have been porting several project test suites over to GitHub Actions, and I encountered a strange behaviour on the windows-2019 image: running a trivial unittest-based test suite, Python exits with an exit code of 1 after successfully running just a single test. This behaviour does not occur on Linux, OS X or windows-2016.

I have put together a minimal project (no dependencies, a trivial module which just defines __version__, and two trivial tests) with which systematically triggers the issue:

https://github.com/aiortc/unittest-ga

As you can see the test suite:

• passes for all Python versions on OS X / Linux / Windows 2016
• fails for all Python versions on Windows 2019

The error looks like:

test_first (tests.test_me.MyTest) ... ok
##[error]Process completed with exit code 1.

[jlaine]

After some further investigation, the root cause may well be powershell. I'm not sure how it explains the different behaviour on Windows 2016 vs 2019, but adding shell: bash seems to fix the issue.