`tests/test_file_watcher_integration.py` became flaky after using `force_polling=True`

[llucax]

What happened?

We are having some sporadic failures, specifically in cross-arch tests (both pytest_min and pytest_max), for file watcher integration tests. In particular this test seems to be flaky: tests/test_file_watcher_integration.py::test_file_watcher.

=================================== FAILURES ===================================
______________________________ test_file_watcher _______________________________

tmp_path = PosixPath('/tmp/pytest-of-root/pytest-0/test_file_watcher0')

    @pytest.mark.integration
    async def test_file_watcher(tmp_path: pathlib.Path) -> None:
        """Ensure file watcher is returning paths on file events.

        Args:
            tmp_path: A tmp directory to run the file watcher on. Created by pytest.
        """
        filename = tmp_path / "test-file"

        number_of_writes = 0
        expected_number_of_writes = 3

        file_watcher = FileWatcher(paths=[str(tmp_path)])
        timer = Timer(timedelta(seconds=0.1), SkipMissedAndDrift())

        async for selected in select(file_watcher, timer):
            if selected_from(selected, timer):
                filename.write_text(f"{selected.message}")
            elif selected_from(selected, file_watcher):
                event_type = EventType.CREATE if number_of_writes == 0 else EventType.MODIFY
>               assert selected.message == Event(type=event_type, path=filename)
E               AssertionError: assert Event(type=<EventType.MODIFY: <Change.modified: 2>>, path=PosixPath('/tmp/pytest-of-root/pytest-0/test_file_watcher0')) == Event(type=<EventType.CREATE: <Change.added: 1>>, path=PosixPath('/tmp/pytest-of-root/pytest-0/test_file_watcher0/test-file'))
E                 
E                 Differing attributes:
E                 ['type', 'path']
E                 
E                 Drill down into differing attribute type:
E                   type: <EventType.MODIFY: <Change.modified: 2>> != <EventType.CREATE: <Change.added: 1>>
E                 
E                 Drill down into differing attribute path:
E                   path: PosixPath('/tmp/pytest-of-root/pytest-0/test_file_watcher0') != PosixPath('/tmp/pytest-of-root/pytest-0/test_file_watcher0/test-file')

tests/test_file_watcher_integration.py:37: AssertionError

What did you expect instead?

Test to always pass.

Affected version(s)

v1.2.0

Affected part(s)

Unit, integration and performance tests (part:tests)

Extra information

• Failed jobs

  • https://github.com/frequenz-floss/frequenz-channels-python/actions/runs/11030029977/job/30633740881
  • https://github.com/frequenz-floss/frequenz-channels-python/actions/runs/10995292713/attempts/1

• Tips

  • We are using some small times in those tests, in the order of tens or hundreds of milliseconds, since cross-arch tests are sloooooow the flakiness probably comes from there.

[llucax]

Looks like the issue is we are watching the whole test directory.