pytest
Expert guidance for Python testing with pytest framework. Use when (1) writing unit tests or integration tests, (2) setting up test fixtures for setup/teardown, (3) parametrizing tests with multiple inputs, (4) using markers (skip, xfail, custom), (5) mocking/patching with monkeypatch or pytest-mock, (6) configuring pytest (pytest.ini, pyproject.toml, conftest.py), (7) running tests with coverage, (8) debugging test failures, or (9) testing async code, FastAPI, Django, or Flask apps.