test-driven-development

Test-driven development starts with writing a failing test before implementation. Follow the red-green-refactor cycle: write a test that fails, implement minimal code to pass it, then refactor. This ensures every line of code is verified and maintains test coverage throughout development.

Writing tests first clarifies requirements, prevents bugs before they ship, and guides design. Test-first development catches regressions early, reduces debugging time, and ensures code reliability by requiring proof that each feature works as intended.

To fix a bug with TDD, write a failing test that reproduces the bug, confirm the failure, then implement the minimal fix to pass the test. This guarantees the fix works and prevents the same bug from reoccurring in future code changes.

TDD prevents anti-patterns like testing mock behavior instead of real functionality, using incomplete mocks, and adding test-only methods to production code. By enforcing a failing test first, it ensures tests verify actual behavior rather than implementation details.

Yes. During refactoring, TDD ensures code changes maintain correctness by keeping tests green throughout. Write tests for the existing behavior first, refactor with confidence that tests catch any regressions, and maintain design quality while improving code structure.

TDD writes failing tests first, then implements code—tests drive design and requirements. Writing tests after code often tests implementation rather than behavior, misses edge cases, and provides weaker design guidance. TDD improves code quality and reliability from the start.