TDD is a development approach where you write tests before writing code, then write just enough code to make tests pass—a cycle called Red-Green-Refactor.
Why It Matters
TDD catches bugs early, ensures tests actually test what matters, and creates a safety net that enables confident refactoring and long-term maintainability.
When to Use This
- Writing tests that define expected behavior first
- Ensuring new features don't break existing functionality
- Documenting expected behavior through tests
- Enabling confident refactoring
Examples
- Writing test for user registration before implementing it
- PHPUnit tests verifying API endpoint responses
- Browser tests confirming checkout flow works end-to-end