tdd

Test-driven development is a test-first implementation approach using the red-green-refactor cycle to arrive at behaviorally correct code. You write a failing test, produce minimal code to pass it, then safely refactor only after reaching green.

To implement a feature using test-driven development, apply vertical slicing by outlining one behavior end-to-end and creating a single focused test. Use tracer bullets to prove the path works, write minimal code to satisfy the current test, then refactor with guardrails.

Use test-first implementation when adding new features or fixing bugs to prevent regressions and guide design toward testable interfaces. Applying test-driven development helps you implement behavior safely by verifying through public interfaces before expanding coverage.

Yes, this test-driven development workflow supports mocking and specification-by-example. It emphasizes interface-first design for testability, ensuring dependencies and outputs are structured to make mocking and verification straightforward during the red-green-refactor cycle.

A limitation of test-driven development is that refactoring is restricted to after reaching green, and it requires vertical slicing. You must implement one behavior per cycle and verify through public interfaces, avoiding batched tests or premature refactoring that breaks the specification guardrails.