Configures and runs pytest - the de facto Python test framework with fixture-based dependency injection (`@pytest.fixture` with scopes module/session/function), parametrize for table-driven tests (`@pytest.mark.parametrize`), markers (`@pytest.mark.skip` / `xfail` / `slow`), `conftest.py` for shared fixtures, plugin ecosystem (pytest-cov, pytest-asyncio, pytest-mock, pytest-xdist), `--lf`/`--ff` for fail-loop, coverage gating. Use when working with Python and needing the modern test framework.