test-driven-development

Test-driven development begins by writing a minimal failing test that demonstrates desired behavior. You confirm the test fails for the expected reason, implement the smallest code change to pass it, and refactor while keeping the suite green.

The red-green-refactor cycle drives design by first writing a failing test, implementing the minimal code to make it pass, and then refactoring with confidence. It surfaces missing behavior early and prevents unverified production code from shipping.

Test-first bug fixing requires reproducing the defect as a failing test before changing any code. Validating the failure ensures you fix the exact issue, and the passing test stays in the suite to prevent future regressions.

Test-driven development protects refactoring by using tests as living documentation of expected behavior. Keeping the test suite all-green during code changes ensures structural improvements do not alter or break existing software functionality.

When writing tests first, avoid skipping failure validation, writing overly broad tests, or implementing more than the minimal passing change. Following a verification checklist ensures minimal focused tests and a reliable green test suite.