What is Test-Driven Development (TDD)?

Answer

Test-Driven Development (TDD) is a practice where you write a failing automated test before writing the code that makes it pass. The cycle is 'red, green, refactor': write a test that fails (red), write the minimal code to make it pass (green), then clean up the design while keeping tests passing (refactor). This keeps code testable, documents intended behavior, and builds a safety net of regression tests. The trade-off is discipline and upfront effort, which pays off most on logic-heavy code with clear requirements.