I think what he describes is TDD and is actually what TDD is ment to embrace. 1. Write down the API and how it defines first (specification) - Would be Red because we don’t have the specification/API internals implemented yet 2. Implement the easiest solution to make it for (prototype) - Green, after the small iterations you take some tests go green because the meet the created specification 3. make it nice - blue, now that you assured the api is working as intended make its internals nice.