test-driven-development

Test-driven development enforces a red-green-refactor workflow to validate requirements before production code is written. You write a failing test, implement minimal code to pass it, and refactor only after test verification.

The red-green-refactor workflow in unit testing requires writing a failing test first, creating a minimal implementation to make it pass, and then refactoring the code safely only after test verification succeeds.

Test-first development prevents unverified production code by enforcing test quality standards that avoid weak tests, mock-driven testing, unnecessary test-only production code, and incomplete validation during software development.

Test-driven development applies to refactoring and behavior changes by requiring regression validation through automated tests. This ensures every behavior modification is backed by verified tests before implementation changes are introduced.

Writing failing tests before implementing bug fixes is required by this test-first workflow. It validates the bug exists, ensures your fix resolves it, and prevents future regressions through reliable automated tests.

A test-first workflow should not be used when minimal implementations cannot be validated or when automated tests are impossible. It enforces failing-test verification, making it unsuitable for scenarios lacking clear behavior expectations.