test-driven-development

Test-driven development (TDD) is a test-first discipline requiring a minimal failing test before any production code. The red-green-refactor cycle mandates watching the test suite fail, implementing the slightest fix to turn it green, then refactoring while keeping tests passing.

To write a failing test for a new feature or bug fix, define the expected behavior first. You must run npm test to confirm it fails for the expected reason, then write the minimal production code needed to make it pass, avoiding regressions and hidden assumptions.

Yes, test-first development applies to refactoring and behavior changes. You write a failing test that exposes the unmet requirement or desired behavior, confirm the failure, implement the fix, and refactor while ensuring the test suite remains green throughout the process.

The best way to enforce test-first discipline is to mandate writing one minimal failing test per requirement before touching code. Ask for the testing steps upfront, watch npm test fail, implement the slightest fix, and keep implementation minimal until all tests pass.

Watching the test suite fail proves the right behavior is captured and exposes unmet requirements. Running npm test to witness failure ensures each change has an observable failure, preventing false positives and confirming the test actually validates the new production code.