RuntimeError: Event loop is closed

[dimaqq]

After upgrading to pytest==5.4.3 pytest-asyncio==0.14.0 I'm getting transient(?) test failures and all I see in the log is this:

=================================== FAILURES ===================================
___________________________ test_xx ___________________________

kwargs = {'xx': XxFixture(, ...}
 
    @functools.wraps(func)
    def inner(**kwargs):
>       coro = func(**kwargs)
 
/root/.cache/pypoetry/virtualenvs/xx-py3.8/lib/python3.8/site-packages/pytest_asyncio/plugin.py:175: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/root/.cache/pypoetry/virtualenvs/xx-py3.8/lib/python3.8/site-packages/pytest_asyncio/plugin.py:175: in inner
    coro = func(**kwargs)
/root/.cache/pypoetry/virtualenvs/xx-py3.8/lib/python3.8/site-packages/pytest_asyncio/plugin.py:177: in inner
    task = asyncio.ensure_future(coro, loop=_loop)
/usr/local/lib/python3.8/asyncio/tasks.py:661: in ensure_future
    task = loop.create_task(coro_or_future)
/usr/local/lib/python3.8/asyncio/base_events.py:429: in create_task
    self._check_closed()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <_UnixSelectorEventLoop running=False closed=True debug=False>

    def _check_closed(self):
        if self._closed:
>           raise RuntimeError('Event loop is closed')
E           RuntimeError: Event loop is closed

/usr/local/lib/python3.8/asyncio/base_events.py:508: RuntimeError
---------------------------- Captured stdout setup -----------------------------

There are some fragile tests in the project and we use flaky to manage those, so I see this error only when some test fails thrice.
Weirdly I don't get to see the actual test failure/cause in this case.

At the moment I'm at a loss as to how to debug it 🤔

[dimaqq]

MRE: https://github.com/dimaqq/mre-loop-closed

Key circumstances: pytest, pytest-asyncio, flaky and failing test.
Instead of a failure, an error is reported.
In fact, first test failure breaks the harness and "flaky" test is not retried.

[dimaqq]

A curious observation, when the test is annotated @flaky(max_runs=10), the error backtrace has 10 (or possibly 10 - 1) levels of pytest-asyncio coro wrap:

site-packages/pytest_asyncio/plugin.py:175:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
site-packages/pytest_asyncio/plugin.py:175: in inner
    coro = func(**kwargs)
site-packages/pytest_asyncio/plugin.py:175: in inner
    coro = func(**kwargs)
site-packages/pytest_asyncio/plugin.py:175: in inner
    coro = func(**kwargs)
site-packages/pytest_asyncio/plugin.py:175: in inner
    coro = func(**kwargs)
site-packages/pytest_asyncio/plugin.py:175: in inner
    coro = func(**kwargs)
site-packages/pytest_asyncio/plugin.py:175: in inner
    coro = func(**kwargs)
site-packages/pytest_asyncio/plugin.py:175: in inner
    coro = func(**kwargs)
site-packages/pytest_asyncio/plugin.py:175: in inner
    coro = func(**kwargs)
site-packages/pytest_asyncio/plugin.py:177: in inner
    task = asyncio.ensure_future(coro, loop=_loop)
asyncio/tasks.py:661: in ensure_future
    task = loop.create_task(coro_or_future)
asyncio/base_events.py:429: in create_task
    self._check_closed()