async-test-uses-sync-testclient

Detects async def test_* functions under tests/ that instantiate TestClient(...).

Why it matters:

• FastAPI / Starlette TestClient is mainly a bridge for synchronous tests calling an async ASGI app.
• Using it inside async tests adds extra sync/async boundaries.
• That can add overhead and make async fixture, lifespan, or shared-resource behavior less predictable.

Suggested action:

• In async tests, use httpx.AsyncClient with ASGITransport.
• If the test does not need to be async, keep it synchronous and use TestClient there.

Measurement:

• Compare pytest runtime before and after the change.
• Check that lifespan handling, DB/session fixtures, and async mocks still behave as expected.

Compatibility notes:

• This rule uses a lightweight source scan, not a full Python parser.
• It is intentionally advisory and may need manual review for unusual test helper patterns.