test-driven-development

Test-driven development starts by writing a failing test that describes your desired behavior, then implementing minimal production code to pass it. This Red-Green-Refactor cycle—fail, pass, refactor—ensures your code is validated by tests from the start and guards against regressions.

Red-Green-Refactor is a three-step cycle: write a failing test (Red), implement minimal code to pass it (Green), then improve code clarity without changing behavior (Refactor). This discipline ensures tests drive design and every feature has test coverage.

Apply test-driven development when implementing new features, fixing bugs, refactoring existing code, or making behavior changes across codebases. Writing failing tests first verifies expectations and prevents regressions in all these scenarios.

Failing tests first enforce test-first discipline, ensuring every change is validated by tests and preventing untested code from entering production. This approach catches regressions early and confirms behavior works as intended.

Yes. Test-driven development works for bug fixes, refactoring, and new features in existing codebases. Write a failing test to capture the desired behavior or bug fix, then implement minimal code to pass—maintaining test-first discipline across your codebase.

Minimal code means implementing only what's necessary to pass the failing test, avoiding speculation or over-engineering. This keeps changes well-scoped, focused on verified behavior, and easier to review and maintain.