test-driven-development

Test-driven development is a test-first workflow requiring a failing test before writing production code. The red-green-refactor cycle works by writing a failing test, implementing minimal code to pass it, and refactoring while keeping tests green.

To use test-first development for bug prevention, write a failing test that describes the new behavior, then implement the smallest amount of production code required to make the test pass before deploying.

Yes, you can apply test-driven development when refactoring existing code. It establishes clear behavior expectations before changes, allowing you to evolve design safely and continuously refactor while keeping tests green.

You need to write a failing unit test as the first step of test-first development. This test defines the expected behavior and ensures correct functionality before any production code is implemented.

Writing production code before tests leads to defects because it lacks enforced behavior expectations. Test-first development solves this by requiring failing tests upfront to catch bugs early and document intent.