Set a shared event loop per test case

Using Django Getting Started
1

Hi all,

Is there a way to use the same event loop for all the tests in a class? We are facing an issue related to using the Strict Redis async client (we don’t use Django Redis client). Currently, we need to create a new Redis client for each test because Django creates a different event loop. This behavior is similar to IsolatedAsyncioTestCase. However, we would prefer to use a single event loop shared by all tests, eliminating the need to create multiple Redis clients.

Has anyone faced this issue?

Kind regards!

2

(This probably belngs in the “Using Django” category?)

Firstly, this is why your tests are running in their own event loops.

Over in django/test/testcases.py::SimpleTestCase._setup_and_call:


        # Convert async test methods.
        if iscoroutinefunction(testMethod):
            setattr(self, self._testMethodName, async_to_sync(testMethod))

async tests are just wrapped in async_to_sync (which spins up its own event loop at the point of decoration)

        # from AsyncToSync.__init__
        self.main_event_loop = None
        try:
            self.main_event_loop = asyncio.get_running_loop()
        except RuntimeError:
            # There's no event loop in this thread.
            pass

One idea: figure out how to get an event loop set up by the time test collection by the test runner is happening. I don’t know what would make sense there, and it’d be a hack.

Another idea: write yourself a decorator for your async tests. Bit silly but would at least be a touch more principled.

import asyncio
import functools

test_loop = asyncio.new_event_loop()

def share_event_loop(test):
    @functools.wraps(test)
    def wrapped(*args, **kwargs):
        coro = test(*args, **kwargs)
        return test_loop.run_until_complete(coro)
    return wrapped

Then in your test case:

class MyTestCase(TestCase):
    @share_event_loop
    async def test_some_async_thing(self):
        ...

This likely doesn’t handle much though.

3

At first glance, I think it could also be an acceptable change in Django to share the same event loop across a whole test process.

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