Autousing fixtures while testing fns which have explicit type-checks?

[xor-xor]

Let's say that I need to test some function, which explicitly checks the type of its input, and I have no control over this behavior. Also, let's say, that I need a fixture for such test:

import pytest


@pytest.fixture()
def my_fixture():
    return 1


def alien_fun(x):
    assert type(x) == int, "sorry, integers only!"
    return x + 1


def test_alien_fun(my_fixture):
    print(type(my_fixture))

    result = alien_fun(my_fixture)

    assert result == 2

So far, so good - everything works as expected and I get <class 'int'> in the output.

BUT!

If I change this fixture to autouse=True (because e.g. I have a lots of tests like the one above and I just don't want to repeat the same declaration over and over):

import pytest


@pytest.fixture(autouse=True)
def my_fixture():
    return 1


def alien_fun(x):
    assert type(x) == int, "sorry, integers only!"
    return x + 1


def test_alien_fun():
    print(type(my_fixture))

    result = alien_fun(my_fixture)

    assert result == 2

...then everything breaks with AssertionError: sorry, integers only! (well, obviously), because my_fixture is now <class 'function'>.

Assuming that this is a feature, not a bug, my question is: what is the "canonical" way of handling such situations?

EDIT: actually, I've just realized that this type assertion here is irrelevant - this autouse=True case will just "explode" on return x + 1 for exactly the same reason.

[portyu9]

Hi @xor-xor

autouse=True makes pytest execute the fixture automatically. It does not replace the fixture function's Python name with its return value.

So if you write:

@pytest.fixture(autouse=True)
def my_fixture():
    return 123

then inside ordinary module code, my_fixture still refers to the fixture function object.

To receive 123, request the fixture normally:

def test_something(my_fixture):
    assert isinstance(my_fixture, int)

Using autouse=True is mainly useful when a fixture's side effects should happen for every test without adding the fixture argument explicitly.

If you actually need the fixture value, keeping it as an explicit test/fixture argument is the idiomatic approach and also works best with type annotations and IDEs.

Please mark this answer as accepted if it helped, thank you.