test-driven-development

Test-driven development proves code correctness by enforcing a test-first workflow to catch regressions early. You write failing tests first, implement minimal code to pass, then refactor, making behavior visible and preventing future regressions.

To use Red-Green-Refactor for feature development, write a failing test for the target behavior, implement the minimal code required to make that test pass, and then refactor the codebase for clarity while ensuring tests remain green.

You reproduce bugs with tests by applying the Prove-It pattern, which requires writing a failing test that captures the exact buggy behavior before applying any fix. This guards against regressions by validating expected behavior upfront.

Test-driven development is highly applicable to complex refactors because it requires behavior to be validated with tests before changes are committed. This ensures existing functionality remains intact while you restructure the code.

The test pyramid guides software testing by providing a balanced mix of unit, integration, and end-to-end tests. This structure delivers fast, reliable feedback during test-driven development while validating behavior across different application layers.

You should avoid test-first development when dealing with exploratory spikes or throwaway prototypes where validating long-term behavior is unnecessary. It requires a structured approach, so applying it to unstable, rapidly changing concepts adds friction.