<objective Comprehensive testing skill covering TDD workflow, test pyramid strategy, mocking patterns, and coverage guidance. Framework-agnostic patterns applicable to pytest, vitest, jest, and other testing frameworks. This skill emphasizes writing tests that provide confidence without becoming maintenance burdens. Tests should be fast, reliable, and focused on behavior rather than implementation details. </objective <quick start TDD Red-Green-Refactor cycle: 1. RED : Write a failing test first 2. GREEN : Write minimum code to pass 3. REFACTOR : Clean up while tests stay green Test pyramid :…