Using @pytest.fixture(scope="module") with @pytest.mark.asyncio

Question

I think the example below is a really common use case:

create a connection to a database once,
pass this connection around to test which insert data
pass the connection to a test which verifies the data.

Changing the scope of @pytest.fixture(scope="module") causes ScopeMismatch: You tried to access the 'function' scoped fixture 'event_loop' with a 'module' scoped request object, involved factories.

Also, the test_insert and test_find coroutine do not need the event_loop argument because the loop is accessible already by passing the connection.

Any ideas how to fix those two issues?

import pytest

@pytest.fixture(scope="function")  # <-- want this to be scope="module"; run once!
@pytest.mark.asyncio
async def connection(event_loop):
    """ Expensive function; want to do in the module scope. Only this function needs `event_loop`!
    """
    conn await = make_connection(event_loop)
    return conn


@pytest.mark.dependency()
@pytest.mark.asyncio
async def test_insert(connection, event_loop):  # <-- does not need event_loop arg
    """ Test insert into database.

        NB does not need event_loop argument; just the connection.
    """
    _id = 0
    success = await connection.insert(_id, "data")
    assert success == True


@pytest.mark.dependency(depends=['test_insert'])
@pytest.mark.asyncio
async def test_find(connection, event_loop):  # <-- does not need event_loop arg
    """ Test database find.

        NB does not need event_loop argument; just the connection.
    """
    _id = 0
    data = await connection.find(_id)
    assert data == "data"

Asked By: Daniel Farrell

||

Source

Answer 1

The solution is to redefine the event_loop fixture with the module scope. Include that in the test file.

@pytest.fixture(scope="module")
def event_loop():
    loop = asyncio.get_event_loop()
    yield loop
    loop.close()

Answered By: Daniel Farrell

Answer 2

Similar ScopeMismatch issue was raised in github for pytest-asyncio (link). The solution (below) works for me:

@pytest.yield_fixture(scope='class')
def event_loop(request):
    loop = asyncio.get_event_loop_policy().new_event_loop()
    yield loop
    loop.close()

Answered By: shrey khare

Answer 3

The event loop of pytest-asyncio was, up until version 0.23.0, running within the scope of a "function". This made it so that you had to override the actual event_loop and give it a bigger scope (see accepted answer).

However, since 0.23.0 this has been deprecated, and it now supports passing the scope of the event loop directly to the asyncio mark of the test in question:

@pytest.mark.asyncio(scope="module")
async def test_find(connection):
    pass

ref: https://pytest-asyncio.readthedocs.io/en/latest/concepts.html#asyncio-event-loops

Answered By: gosuto

Using @pytest.fixture(scope="module") with @pytest.mark.asyncio

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