Configuration option for a custom event loop policy and/or custom event loop class?

[leifurhauks]

It would be useful when testing an application that uses a custom implementation of asyncio.AbstractEventLoop to be able to provide a custom event loop policy and/or custom event loop via a configuration option.

It is of course already possible to set the event loop policy globally with asyncio.set_event_loop_policy (e.g. in pytest_configure) or to override the event_loop fixture so that it returns a loop of the desired class, so perhaps this would be unnecessary.

[Tinche]

I agree being able to test using a different event loop can be useful.

I'd argue the approach most in the spirit of pytest would be to override the event_loop fixture. This will make the pytest.mark.asyncio marker use the overriden loop as well. This should be documented in the README, along with an example.

[imposeren]

maybe something like fixture factory may be used?

def event_loop_fixture_factory(default_policy=None):
    @pytest.fixture
    def event_loop_fixture(request):
        """Create an instance of the default event loop for each test case."""
        policy = default_policy or asyncio.get_event_loop_policy()

        policy.get_event_loop().close()

        event_loop = policy.new_event_loop()
        policy.set_event_loop(event_loop)

        request.addfinalizer(event_loop.close)
        return event_loop

    return event_loop

event_loop = event_loop_fixture_factory()

[Tinche]

Hi,

we've already sketched out a solution in #21 and there's an implementation in https://github.com/pytest-dev/pytest-asyncio/tree/feature/pluggable-event-loops. I just need to write the docs before merging it in and doing a release.

I'm pretty happy with the results.

[Tinche]

I believe this is fixed in 0.4, open another issue for further discussion if you feel like it.