testing-fundamentals

Test-driven development (TDD) follows a Red-Green-Refactor cycle: write a failing test, implement minimal code to pass it, then refactor for quality. This approach enforces testing discipline, catches bugs early, and ensures 80%+ test coverage while protecting critical paths and validating error handling.

Unit tests verify individual functions in isolation; integration tests validate component interactions; end-to-end tests confirm full user workflows. TDD applies the Arrange-Act-Assert pattern across all three types, ensuring comprehensive coverage from function logic through system behavior.

Coverage targets require systematic testing of critical paths, error conditions, and edge cases. Combine unit tests for functions, integration tests for component interactions, and end-to-end tests for user scenarios. Refactor code to eliminate untested branches and continuously analyze coverage metrics.

Yes. TDD provides a safety net during refactoring: existing tests verify that behavior remains correct while you restructure code. Write tests covering current functionality first, refactor incrementally, and rerun tests after each change to catch regressions immediately.

Pre-production validation requires testing critical paths, error handling, and edge cases across unit, integration, and end-to-end layers. Verify that all critical functionality has corresponding tests, coverage meets 80%+ targets, and failure scenarios are handled gracefully.