Autouse fixtures in Packages (__init__.py)

Autouse fixtures defined in package __init__.py files are not being executed for tests under the package.

Consider:

# content of pkg/__init__.py
import pytest

values = []

@pytest.fixture(scope="module", autouse=True)
def startup():
    values.append("started")

# content of pkg/test_x.py
from . import values

def test_x():
    assert values == ['started']

This fails because startup() is never called.

If however we replace startup by a xunit-style setup_module function:

# content of pkg/__init__.py
import pytest

values = []

# @pytest.fixture(scope="module", autouse=True)
# def startup():
#     values.append("started")

def setup_module():
    values.append("started")

Then the test passes.

Discovered this bug while working on #3094. 😬

As discussed below, we have to discuss if this is a bug or not.

Reproduce the example using pkg/init.py and pkg/test_x.py, comparing the autouse fixture with setup_module. Then inspect pytest's fixture discovery and package collection behavior to determine whether package-level autouse fixtures are intended to run, and add regression coverage only after the expected behavior is resolved.