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How to timeout an async test in pytest with fixture?

I am testing an async function that might get deadlocked. I tried to add a fixture to limit the function to only run for 5 seconds before raising a failure, but it hasn’t worked so far.

Setup:

pipenv --python==3.6
pipenv install pytest==4.4.1
pipenv install pytest-asyncio==0.10.0

Code:

import asyncio
import pytest

@pytest.fixture
def my_fixture():
  # attempt to start a timer that will stop the test somehow
  asyncio.ensure_future(time_limit())
  yield 'eggs'


async def time_limit():
  await asyncio.sleep(5)
  print('time limit reached')     # this isn't printed
  raise AssertionError


@pytest.mark.asyncio
async def test(my_fixture):
  assert my_fixture == 'eggs'
  await asyncio.sleep(10)
  print('this should not print')  # this is printed
  assert 0

—

Edit: Mikhail’s solution works fine. I can’t find a way to incorporate it into a fixture, though.

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Answer

Convenient way to limit function (or block of code) with timeout is to use async-timeout module. You can use it inside your test function or, for example, create a decorator. Unlike with fixture it’ll allow to specify concrete time for each test:

import asyncio
import pytest
from async_timeout import timeout


def with_timeout(t):
    def wrapper(corofunc):
        async def run(*args, **kwargs):
            with timeout(t):
                return await corofunc(*args, **kwargs)
        return run       
    return wrapper


@pytest.mark.asyncio
@with_timeout(2)
async def test_sleep_1():
    await asyncio.sleep(1)
    assert 1 == 1


@pytest.mark.asyncio
@with_timeout(2)
async def test_sleep_3():
    await asyncio.sleep(3)
    assert 1 == 1

It’s not hard to create decorator for concrete time (with_timeout_5 = partial(with_timeout, 5)).

I don’t know how to create texture (if you really need fixture), but code above can provide starting point. Also not sure if there’s a common way to achieve goal better.

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