Test Driven Development (TDD), good idea in theory, but in practice? Carl and Richard talk to John Callaway and Clayton Hunt about their success with TDD. At it's simplest level, TDD is about writing tests first, before coding. In practice, everything is more complicated than that. Writing testable code isn't as simple as it seems, and refactoring existing code to become testable can cause it to break - which is why you wanted tests in the first place. John and Clayton talk through their experiences getting things right and exploring the advantages that TDD brings - more reliable software that sustains for longer and can continue to evolve!