Test-Driven Development (TDD)

Test-driven development is a methodology where you write failing tests before implementing features, ensuring code meets requirements from the start. This approach catches bugs early, documents expected behavior, and produces more reliable, maintainable code with fewer regressions.

Write a failing test that specifies the desired behavior, verify it fails for the right reason, implement minimal code to pass the test, confirm all tests pass, then refactor without changing external behavior. This cycle ensures each feature is tested and verified before completion.

Run your test suite before any implementation to confirm tests fail. This verification proves your tests exercise the right code path and will catch real bugs. Without this step, tests may pass for the wrong reasons and miss actual failures.

Yes. Write a failing test that reproduces the bug, verify it fails, apply minimal changes to fix it, then refactor if needed. This ensures the bug stays fixed and prevents regressions on the same code path.

Unit tests verify individual functions or components in isolation, while integration tests verify real behavior across module boundaries. TDD emphasizes behavioral testing at integration boundaries to ensure features work end-to-end, not just mocks in isolation.

Refactor only after tests pass. Focus on improving code clarity, removing duplication, and simplifying logic without changing external behavior. Refactoring with a passing test suite ensures changes don't break functionality.