TDD

TDD is a software development process that relies on a tight 'Red-Green-Refactor' loop to ensure code correctness and design quality.

TDD flips traditional development by requiring a failing unit test before any production code is written. Engineers follow a strict three-step cycle: write a test that fails (Red), write the minimum code necessary to pass (Green), and optimize the structure (Refactor). This discipline reduces bug density by up to 40% to 90% compared to manual testing (per Microsoft and IBM research) and creates a self-documenting suite of tests. By focusing on requirements before implementation, teams avoid over-engineering and maintain high velocity in complex codebases.

https://martinfowler.com/bliki/TestDrivenDevelopment.html