OpenEdxEventsTestMixin interferes with other test cases

[bradenmacdonald]

If one test class in a given test run uses OpenEdxEventsTestMixin, and other tests in the same test run use events but do not use OpenEdxEventsTestMixin, then the other tests will sometimes fail in a flaky fashion, depending on the order that the tests are run.

This is because OpenEdxEventsTestMixin disables all signals, then enables the subset ENABLED_OPENEDX_EVENTS, then runs the tests - but it does not clean up. It should have a clean up handler like this:

    @classmethod
    def tearDownClass(cls):
        """ Don't let our event isolation affect other test cases """
        super().tearDownClass()
        cls.enable_all_events()

[bradenmacdonald]

I've put some changes in openedx/edx-platform#36640 to work around this for now: openedx/edx-platform@281bb5b and openedx/edx-platform@f725245 but once the post-Teak dust has settled, I think we should do a proper fix in the base class, and ideally avoid the need for derived classes to override setUpClass and tearDownClass at all.

[mariajgrimaldi]

Thank you for bringing this up, @bradenmacdonald! Also for finding a workaround for teak. I'll assign this to myself to work on once we get the release out.

[bradenmacdonald]

Great, thanks @mariajgrimaldi !