Is it possible to use a fixture inside pytest_generate_tests()?

Question

I have a handful of fixtures in conftest.py that work well inside actual test functions. However, I would like to parameterize some tests using pytest_generate_tests() based on the data in some of these fixtures.

What I'd like to do (simplified):

-- conftest.py --
# my fixture returns a list of device names.
@pytest.fixture(scope="module")
def device_list(something):
    return ['dev1', 'dev2', 'dev3', 'test']

-- test001.py --
# generate tests using the device_list fixture I defined above.
def pytest_generate_tests(metafunc):
    metafunc.parametrize('devices', itertools.chain(device_list), ids=repr)

# A test that is parametrized by the above function.
def test_do_stuff(devices):
    assert "dev" in devices

# Output should/would be:
dev1: pass
dev2: pass
dev3: pass
test: FAIL

Of course, the problem I'm hitting is that in pytest_generate_tests(), it complains that device_list is undefined. If I try to pass it in, pytest_generate_tests(metafunc, device_list), I get an error.

E   pluggy.callers.HookCallError: hook call must provide argument 'device_list'

The reason I want to do this is that I use that 'device_list' list inside a bunch of different tests in different files where I want to use pytest_generate_tests() to parametrize test using the same list.

Is this just not possible? What is the point of using pytest_generate_tests() if I have to duplicate my fixtures inside that function?

Answer 1

From what I've gathered over the years, fixtures are pretty tightly coupled to pytest's post-collection stage. I've tried a number of times to do something similar, and it's never really quite worked out.

Instead, you could make a function that does the things your fixture would do, and call that inside the generate_tests hook. Then if you need it still as a fixture, call it again (or save the result or whatever).