test-driven-development

To start writing failing tests before implementation code, follow the Red-Green-Refactor cycle by creating a failing test first, writing minimal production code to pass it, and then refactoring.

The Red-Green-Refactor cycle is a test-driven development process where you write a failing test (Red), implement minimal code to make it pass (Green), and then clean up the code without changing behavior (Refactor).

Test-driven development prevents regressions in agile workflows by mandating strict test creation prior to writing production code, ensuring every feature is verifiable and robust against future changes.

You should use test-driven development when building new features, such as a user authentication module, to establish strict development discipline, ensure code quality, and prevent untested code paths.

The best way to enforce TDD principles during refactoring is to rely on pre-existing failing tests that validate behavior, ensuring your structural changes improve code quality without introducing regressions.

Applying test-driven development to existing untested code addresses the problem of poor test coverage by establishing strict discipline, requiring you to write verifying tests for current behavior before modifying the code.