Provide async getfixturevalue() method on anyio

[chbndrhnns]

Things to check first

• I have searched the existing issues and didn't find my feature already requested there

Feature description

Pytest allows to retrieve a fixture value by injecting the fixture as a function argument or by using request.getfixturevalue(). The latter fails to provide the value of an async fixture.

import pytest

pytestmark = pytest.mark.anyio


@pytest.fixture
def anyio_backend():
    return "asyncio"


@pytest.fixture
async def f():
    return 1


async def test_problem(request):
    assert request.getfixturevalue('f') == 1

async def test_ok(f):
    assert f == 1

Use case

According to the docs [1], getfixturevalue() runs a fixture dynamically. This feature is not available in anyio currently for async fixtures. However, I would like to make use of it to decide if I need to run a specific fixture based on the value of another fixture.

From the docs:

Dynamically run a named fixture function.

Declaring fixtures via function argument is recommended where possible. But if you can only decide whether to use another > fixture at test setup time, you may use this function to retrieve it inside a fixture or test function body.

[1] https://docs.pytest.org/en/7.1.x/reference/reference.html