pytest-queryguard: ORM-level N+1 detection for SQLAlchemy 2 tests

[MaciejZiel]

Hi! I've been working on pytest-queryguard and could use some feedback from other pytest users.

It catches N+1 queries in SQLAlchemy 2 and fails the test. In #14344, @RonnyPfannschmidt mentioned wanting this at the ORM level. That's what I'm trying here.

I didn't want to require query-count assertions for each test. Instead, I listen to do_orm_execute. SQLAlchemy tells me which relationship is being lazy-loaded and for which parent. The test fails once two different parents lazy-load the same relationship. There are no expected counts to update.

If you want a query limit, you can add @pytest.mark.max_queries(n). It's optional. You can use sync or async sessions, and FastAPI's TestClient works too. I've also added a missing-index check for PostgreSQL 16+. That check is off unless you enable it.

It's on PyPI, and the code is on GitHub. I also wrote a post about how it works.

I'm still unsure where to draw the line with fixtures. Right now I only watch the test body, using a pytest_runtest_call wrapper. I leave fixture setup out. Would you want me to count queries from fixtures too?

There are also two cases I don't catch. If the identity map handles a lazy load, there's no SQL for me to see. I also miss eager loads that never get used. Have you tried tracking either of these? I'd be interested to hear what worked.