test-driven-development

The Red-Green-Refactor cycle in test-driven development is a workflow where you write a failing test first, write minimal implementation code to make it pass, and then refactor the code to ensure quality. This cycle verifies behavior and enforces rigorous development practices.

To write a failing test before implementation code, you describe the desired behavior of a new feature in your test suite first. This confirms the test's validity by ensuring it fails initially before you write any production code to make it pass.

Your test needs to fail before implementation begins to confirm the test's validity and ensure it is actually checking the desired behavior. Mandating an initial failure prevents false positives when building reliable software.

Yes, you can use test-driven development for agile refactoring to safely improve code quality. By following the Red-Green-Refactor cycle, you ensure that your refactoring efforts do not break existing behavior and continue to meet software requirements.

You should not use the test-first development approach when exploring experimental code spikes or when the expected behavior is entirely undefined. The methodology requires clear requirements to write meaningful failing tests before writing implementation code.