Design for Test

As developers, we're expected to turn out implementations proven by tests that we or others have written. Doing otherwise is considered unprofessional. But does code that's designed to be testable differ fundamentally from code that isn't? What does it mean to design for test? Advocates of test-driven development (TDD) write tests before implementing any other code. They take to heart Tom Peters' credo, "Test fast, fail fast, adjust fast." Testing guides their design as they implement in short, rapid-fire "write test code - fail the test - write enough code to pass - then pass the test" cycles. Regardless of whether you adhere to TDD design rhythms, writing unit tests forces you to articulate pesky edge cases and clean up your design.