test-driven-development

Test-driven development is a workflow where you write a failing test, implement the minimal code to make it pass, then refactor without changing behavior. The Red-Green-Refactor loop enforces this cycle to build features with verified passing behavior and regression safety.

Start writing unit tests by creating a single focused failing test that proves what must work, then write the minimal production code to pass it. Verify the test fails for the right reason, passes with a clean signal, and refactor while keeping the test green.

Test-driven development requires verification discipline: explicitly confirm tests fail for missing features and pass without extra errors or warnings. Without verifying failure reasons and clean signals, tests may pass while masking unverified behavior or incorrect side effects.

Avoid mocking in unit testing when you do not understand required side effects, or when testing mock existence rather than behavior. Test-driven development guardrails prevent mock-focused development and adding test-only methods to production code to ensure meaningful test coverage.

Test-driven development applies to bug fixes and refactoring where correctness and regression safety matter. You start from a failing test proving the required fix, implement the smallest change, then refactor while keeping the test green to maintain verified passing behavior.