Clarify docs about requesting the event_loop fixture

[tuukkamustonen]

https://pytest-asyncio.readthedocs.io/en/latest/reference/fixtures/index.html#event-loop suggests that it's fine to grab event_loop fixture in a non-async function.

0.21+ migration guide in https://pytest-asyncio.readthedocs.io/en/latest/how-to-guides/migrate_from_0_21.html suggests to convert all sync functions requesting the event_loop fixture into async functions, and then acquire the loop via asyncio.get_running_loop().

Which one is it, and what is the rationale of not depending on the event_loop fixture directly?

[seifertm]

The use of event_loop is deprecated. We should adjust the docs to reflect that.
The rationale is summarized here:
#706 (comment)

[tuukkamustonen]

Slowly getting back here.

The thing why I'm asking is that currently we do something like:

def some_fixture(event_loop):
    # do some sync stuff etc...
    # then trigger async actions:
    event_loop.run_until_complete(...)

Similar pattern is not possible with asyncio.get_running_loop() because:

This function can only be called from a coroutine or a callback.

Being able to run invocations in the event loop in a sync function is convenient, as we don't have 100% async codebase, and tests are mostly written in sync.

Do you see the use case here @seifertm? Is the advice to convert the usages to async and then asyncio.to_thread() to sync parts, instead?

[seifertm]

The migration guide suggests converting such tests to async tests and use get_running_loop inside the async test. Following your example:

@pytest_asyncio.fixture()
async def some_fixture():
    # do some sync stuff etc...
    # then trigger async actions:
    event_loop = asyncio.get_running_loop()
    event_loop.run_until_complete(...)

You could possibly even skip asyncio.get_running_loop() in favour of:

@pytest_asyncio.fixture()
async def some_fixture():
    # do some sync stuff etc...
    # then trigger async actions:
    await ...

@tuukkamustonen Do any of those approaches work for your code base?