Test Driven Development
Writing tests before code to guide implementation
Test Driven Development is a software development practice where developers write automated tests before writing the code being tested. This test-first approach guides implementation, ensures testability, and maintains comprehensive test coverage. The TDD cycle follows Red-Green-Refactor: write a failing test for desired behavior, write minimum code to make test pass, and refactor code while keeping tests green. This rhythm repeats for each small piece of functionality. Writing tests first forces developers to think about design and requirements before implementation, ensures code is testable by design, provides immediate feedback on correctness, builds comprehensive test suite, and documents expected behavior through tests. TDD contrasts with writing tests after code, which often results in poorly designed tests, incomplete coverage, and code that's difficult to test. Benefits include higher code quality through early defect detection, better design through testability requirements, comprehensive test coverage, confidence in refactoring with safety net, living documentation through tests, and reduced debugging time. TDD is particularly effective for complex logic, critical functionality, and long-lived codebases. Challenges include initial learning curve, time investment upfront, difficult to retrofit to existing code, and requiring discipline to maintain practice. Not all code benefits equally from TDD; some exploratory or UI code may not warrant test-first approach. Best practices include keeping tests small and focused, writing tests at appropriate level, maintaining fast test execution, refactoring both code and tests, and using TDD for appropriate contexts not dogmatically everywhere. Common mistakes include writing too many tests before code, testing implementation details rather than behavior, or abandoning practice under pressure. Product managers should understand TDD benefits for quality and velocity, support time for test writing, appreciate that TDD can initially feel slower but improves long-term speed, and recognize that comprehensive tests enable confident iteration. Strong TDD practice improves code quality, reduces defects, and enables sustainable development pace.
Understand Test Driven Development in software engineering. Learn how writing tests first improves code quality and design.