Pytest Test Structure

Enforces pytest best practices in Python test suites. Auto-activates on: pytest, test, fixture, mock, assert, coverage. Prevents test interdependence, missing fixtures, unclear assertions, slow tests (>1s unit), setup duplication. Ensures AAA pattern (Arrange-Act-Assert), fixture scoping, parametrize for cases, descriptive names (test_should_*). Validates conftest.py usage, @pytest.mark usage, 80%+ coverage, isolated tests. Targets: <100ms unit tests, 0 test order dependencies, 100% isolated.