test-driven-development

Test-driven development prevents regressions by enforcing a test-first workflow: write a failing test that captures the intended behavior, implement the minimal production change to pass it, and refactor only after all tests pass.

The red-green-refactor loop in TDD involves writing a minimal failing test to validate the red state, implementing the smallest code change to achieve a green passing state, and then refactoring while keeping behavior unchanged.

Write a failing unit test by defining one minimal test that demonstrates the missing behavior, verify the failure occurs for the expected reason, then implement only the production code required to make that specific test pass.

Use a test-first workflow whenever correctness must be proven and regressions prevented before code review or merge, applying it to new features, bug fixes, refactors, and behavior changes to stop common shortcuts like adapting existing code.

Yes, test-driven development works for fixing bugs and changing behavior by requiring you to write a failing test that captures the single behavior you intend to deliver before writing or changing any production code.