test-driven-development

Apply TDD by writing a failing test first, verifying its failure reason, adding minimal production code until it passes, then refactoring while keeping tests green. This enforces strict sequencing to prevent regressions in deterministic library utilities and API methods.

Use test-first development when behavior is deterministic, reused across multiple call sites, and regressions should trip CI. Apply it to library utilities, validators, and API methods to enforce regression prevention through a failing test before implementation.

The correct TDD sequence is RED-GREEN-REFACTOR: write a failing test, verify the failure reason, implement the smallest code change to pass the test, then refactor while keeping the full test suite green. This strict order prevents tests-after patterns.

No, you should not adapt existing code while writing tests. Adapting production code before or during test creation violates the tests-first final rule and breaks the strict RED-GREEN-REFACTOR sequencing required for reliable regression prevention and CI gating.

Ensure CI gating fails on regressions by writing a failing unit test first, verifying the specific failure reason, implementing minimal code to pass, and running the full test suite. This RED-GREEN-REFACTOR loop guarantees CI catches deterministic behavior changes.