How to use setUp from pytest as an async method?

Question

I have the following code:

import asyncio
import pytest

from mymodule import myasyncfunction
from unittest import TestCase


class TestDummy(TestCase):
    def setUp(self):
        await myasyncfunction()

    @pytest.mark.asyncio
    async def test_dummy(self):
        assert False

The test passes because it doesn't enter the test at all. It only says:

RuntimeWarning: coroutine 'TestDummy.setUp' was never awaited

How to make the setUp function async?

Observation: If I remove the inheritance from TestCase the test runs but it won't enter the setUp function before, which is needed.

Answer 1

The solution is to define a method as a fixture instead of using the traditional setUp() method.

import pytest

class TestClass:
    @pytest.fixture
    def setup(self):
        pass

    @pytest.mark.asyncio
    async def test_some_stuff(setup):
        pass

As you discovered, with pytest-asyncio the setUp() method doesn't work when a class inherits from Unitest.Testcase:

TestPersonClass is not a child class of unittest.TestCase. If it was, the test would still succeed – but the success would be a false positive because code after the await expression would not run.

Why is this happening? The answer is complex enough that it deserves a separate post, but the tl;dr version is that on line 93 of pytest-asyncio’s source the author is expecting the event loop to be passed into the test from a pytest fixture, while unittest.TestCase methods cannot directly receive fixture function arguments.

For the above explanation see end of this blog post: https://jacobbridges.github.io/post/unit-testing-with-asyncio/

For some decent tutorials on testing with pytest-asyncio see: 1)https://www.roguelynn.com/words/asyncio-testing/ 2)https://medium.com/ideas-at-igenius/testing-asyncio-python-code-with-pytest-a2f3628f82bc