test-driven-development

Test-driven development is a workflow where you write a minimal failing test, implement the smallest code change to pass it, then refactor while keeping tests green. This enforces behavior specification and validation before production code exists.

To start writing unit tests before implementation, write a minimal failing test expressing desired behavior, verify it fails for the expected reason, implement the smallest change to pass, and maintain green tests throughout refactoring.

Unit tests passing immediately often indicate they validate mocks instead of real behavior. Verification discipline in test-driven development requires watching tests fail for the right reason to ensure they actually test production code behavior.

Use test-driven development for bug fixes, behavior changes, and refactoring efforts where regression prevention and confidence are priorities. It targets codebases with automated test suites to ensure behavior is preserved through refactors.

Test-driven development targets codebases with automated test suites. Without existing test infrastructure, the red-green-refactor workflow lacks the foundation needed to verify failures and maintain green tests during refactoring.

The best way to maintain green tests during refactoring is following the red-green-refactor cycle: write minimal failing tests, implement the smallest change to pass, then refactor incrementally while continuously verifying tests stay green.