Test-Driven Development: Writing Tests First as a Design Tool

Test-Driven Development reverses the usual workflow by writing a failing test before the code it exercises exists. The article argues that this turns tests into executable specifications that shape an API's design rather than merely confirming existing behavior. TDD is described as a development process rather than an architecture, though it tends to push code toward loosely coupled, injectable designs similar to Clean or Hexagonal Architecture. The core workflow is a short Red-Green-Refactor cycle: write a failing test, make it pass with minimal code, then clean up the design while the tests guard against regressions.