tdd

Test-driven development starts by writing a failing unit test first, implementing minimal code to pass, and refactoring while maintaining green tests. This RED-GREEN-REFACTOR cycle reduces debugging time and clarifies specifications before implementation begins.

The RED-GREEN-REFACTOR cycle enforces writing a failing test (RED), writing minimal code to pass (GREEN), and improving code structure (REFACTOR) while keeping tests green. This cycle drives reliable implementations and prevents defects during feature development.

Test-driven development works with standard testing libraries like Jest across various languages and frameworks. The approach requires clear test naming conventions and integrates into CI pipelines that report mutation scores and coverage metrics for comprehensive software quality assurance.

The Prove-It Pattern reproduces bugs by writing failing tests that verify the defect before fixing code. This test-driven approach guards against regressions by ensuring every bug has corresponding test coverage proving the fix works and preventing future recurrence.

Mutation testing improves code quality within test-driven development by measuring test effectiveness through code mutations. A CI pipeline reporting mutation scores validates that tests genuinely catch defects rather than merely achieving superficial coverage metrics.

Mocks and stubs serve different roles in test-driven development: stubs provide controlled responses to satisfy code execution, while mocks verify interactions occurred correctly. The test pyramid guides their appropriate usage across unit and integration testing workflows.