test-driven-development

Test-driven development (TDD) is a test-first workflow enforcing the red-green-refactor cycle: write a minimal failing automated test, implement minimal code to pass it, then refactor while keeping tests green to prevent regressions.

To write unit tests first for a new feature, define the desired behavior with a minimal failing automated test, run the suite to confirm the expected failure, implement the minimal production code to pass, and preserve tests during refactoring.

Use a test-first approach for bug fixes, refactoring, and behavior changes to clarify intended outcomes and reduce technical debt by ensuring every production change is specified by a failing automated test before implementation.

Yes, watching unit tests fail before writing implementation code is mandated by the test-driven development workflow to verify the test actually validates the specified behavior and prevents false positives.

Writing tests before implementation prevents regressions, clarifies intended behavior, and reduces technical debt by ensuring every production change is specified by a failing automated test.

Yes, you can use test-driven development for modifying existing code behavior by writing a failing automated test that demonstrates the desired new outcome before changing the production code.