Python coverage for async methods

Question

I use aiohttp, pytest and pytest-cov to get coverage of my code. I want to get better coverage< but now I am a little bit stuck, because event simple code does not show 100% cov. For example this piece of code:

@session_decorator()
async def healthcheck(session, request):
    await session.scalar("select pg_is_in_recovery();")
    return web.json_response({"status": "ok"})

in coverage report it shows that line with return is not covered.

I have read this link Code coverage for async methods. But this is for C# and I can not understand:

This can happen most commonly if the operation you're awaiting is completed before it's awaited.

My code to run tests:

python3.9 -m pytest -vv --cov --cov-report xml --cov-report term-missing

My test for code above

async def test_healthz_page(test_client):
    response = await test_client.get("/healthz")
    assert response.status == HTTPStatus.OK

How did your unittest invoke the healthcheck function? You may need to adapt your test case methods such that they execute as intended, please take a look at this thread on how this may be done. — metatoaster
– metatoaster, Commented Aug 18, 2021 at 5:24
You will need to mark your test correctly with pytest, see thread and thread and thread for examples. — metatoaster
– metatoaster, Commented Aug 18, 2021 at 5:54
Pytest doesn't have built-in support for async tests. What plugin do you use for that, pytest-asyncio or something else? — hoefling
– hoefling, Commented Aug 18, 2021 at 6:09
To clarify: the code after the first await is never shown as covered. — bfontaine
– bfontaine, Commented Apr 11, 2023 at 14:45

bfontaine · Accepted Answer · 2023-04-17 10:22:22Z

13

I had the same issue when testing FastAPI code using asyncio. The fix is to create or edit a .coveragerc at the root of your project with the following content:

[run]
concurrency = gevent

If you use a pyproject.toml you can also include this section in that file instead:

[tool.coverage.run]
concurrency = ["gevent"]

In addition, you have to pip install gevent. If using Poetry, run poetry add --group dev gevent.

If the above doesn’t work, try using concurrency = thread,gevent instead (see this comment. Note it says to use --concurrency but this option is not available when you use pytest-cov; you must use .coveragerc).

edited Apr 17, 2023 at 10:22

answered Apr 17, 2023 at 9:59

bfontaine

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