test-driven-development

The RED-GREEN-REFACTOR cycle in test-driven development requires writing a failing test, verifying it fails for the correct reason, implementing minimal code to pass, refactoring, and running the full suite to prevent regressions.

To implement a bugfix with test-first development, write a failing test that reproduces the bug, verify the failure, add the minimal production code to make it pass, then run the full test suite to ensure no regressions.

Yes, you can apply test-driven development across common programming languages and codebases when implementing new behavior, refactoring, or changing existing systems to improve code quality.

Verifying that a failing test fails for the right reason ensures the test targets the actual missing behavior or bug, preventing false positives before you write the minimal implementation to make it pass.

You should prefer tests that validate outcomes with real code rather than relying on brittle mocks, ensuring your test-driven development process verifies actual behavior and reduces regression risk.

You should avoid strict test-first development when exploring experimental prototypes where behavior is undefined, as the RED-GREEN-REFACTOR cycle requires predefined behavior to write meaningful failing tests.