Python testing with pytest using uv package manager. Use when: (1) Running Python tests, (2) Writing test files or test functions, (3) Setting up fixtures, (4) Parametrizing tests, (5) Generating coverage reports, (6) Testing FastAPI applications, (7) Debugging test failures, (8) Configuring pytest options. Triggers: "run tests", "write tests", "test coverage", "pytest", "unit test", "integration test", "test FastAPI".