SafeChildWatcher is not reinstalled properly after the second test is loop fixture is not used

[tardyp]

Long story short

When moving to aiohttp 3.3+, my tests suddently hang at await process.wait()
but only after one test has run previously

Expected behaviour

process.wait() returns when the process finishes

Actual behaviour

process.wait() never returns

Steps to reproduce

pip install aiohttp pytest pytest-aiohttp pytest-asyncio

run the following test suite:

import asyncio


async def test_basic():
    sleep_proc = await asyncio.create_subprocess_exec("sleep", '0.1',)
    await sleep_proc.wait()


async def test_basic2():
    sleep_proc = await asyncio.create_subprocess_exec("sleep", '0.1',)
    await sleep_proc.wait()

The second test will fail.

Your environment

macos python3.7 from brew.

Rootcause start

if I change SafeChildWatcher installer in test_utils.py:setup_test_loop to following code, the test will work

    if sys.platform != "win32" and not skip_watcher:
        policy = asyncio.get_event_loop_policy()
        if not policy.get_child_watcher():
            watcher = asyncio.SafeChildWatcher()
            watcher.attach_loop(loop)
            with contextlib.suppress(NotImplementedError):
                policy.set_child_watcher(watcher)
    return loop

[tardyp]

looks like this comes from this commit:
8e76a4a

if I look at the code, I don't see why it is needed.

asyncio.get_child_watcher() will always automatically create the default safe childwatcher

https://github.com/python/cpython/blame/master/Lib/asyncio/unix_events.py#L1097

[tardyp]

Another fix is to use loop in my test fixtures

[tardyp]

Forgot to update on this.
This issue is fixed by adding loop in the fixture list for each test.