pytest is, in many ways, the Age of Adz of the broader Python ecosystem: a rewarding idiosyncratic departure from convention whose quirks and foibles are quickly and easily outweighed by the fact that it’s just really, really good.

Magic name-based dependency injection? Totally new scoping paradigm? Autodiscovery? Sure. All of that is forgivable because the tests themselves become so pleasant to read and write.

And/but/nevertheless, much like Age of Adz’ impenetrability being in no small part due to track length (Impossible Soul, the closing track, sums to twenty five minutes across five parts; the title track alone is eight minutes) — conftest.py, the vaguely bizarre ur-file which contains all of your fixtures and other various pytest goodies, can quickly get bloated and confusing. 1 ^[1]

What I wanted was the same thing I had for tests — colocation. If I had, say, a survey model, I wanted to be able to define the fixtures for that model next to the model itself but still have it be globally available. Same thing with external services: if I’m mocking out my calls to Stripe, it just makes more sense to organize those mocks closer to the actual implementation code.

I struggled to figure out a way to do this until poking around the docs and realizing that “plugins” are more of a duck type than an actual thing — from pytest’s perspective, a plugin is just a module filled with stuff, and therefore I could technically treat a file filled purely with fixtures as a “plugin” imported by my root conftest.py.

This means I can do something like this:

# /emails/models/survey/model.py
class Survey(BaseModel):
    identifier = models.CharField(max_length=100)
    question = models.CharField(max_length=500)
    answers = ArrayField(base_field=models.CharField(max_length=500))
    newsletter = models.ForeignKey(
        Newsletter, on_delete=models.CASCADE, related_name="surveys"
    )
    
# /emails/models/survey/model--mock.py
@pytest.fixture
def survey(newsletter: Newsletter) -> Survey:
    return Survey.objects.create(
        newsletter=newsletter,
        identifier="pokemon",
        question="What's your favorite starter?",
        answers=["Bulbasaur", "Charmander", "Squirtle"],
        notes="",
    )

# /conftest.py
pytest_plugins = [
    "emails.models.newsletter.model--mock",
    "emails.models.survey.model--mock",
]

There’s no real magic here — well, besides all the magic employed by pytest. But it’s a nice tactic that cut our root conftest from ~2KLOC down to a very manageable 200, and made fixtures much more discoverable in the process.