Use GH actions to test on OSX and Windows as well

[davidbrochart]

No description provided.

[davidbrochart]

Some interesting results: https://github.com/davidbrochart/nbclient/pull/1

[choldgraf]

Haha whoa - I wonder why it isn't running on this PR though?

[davidbrochart]

Yes I don't know why either. And it doesn't run the coverage job.

[choldgraf]

what if you manually set it to on: pull_request, push? Maybe it's the * that is the issue?

[davidbrochart]

Ah it needs the tests to pass before doing code coverage 😄

[davidbrochart]

test_many_parallel_notebooks was failing because it uses multiprocessing (a pool of 2 cores + the main python program). Maybe we only have one core on GH actions?

[davidbrochart]

This is ready to be merged. We are keeping Travis CI anyway, so it's just adding GitHub actions CI, except that we don't use pebble anymore for test_many_parallel_notebooks (for some reason it didn't work on GH actions, and we have the same with concurrent.futures.ProcessPoolExecutor).