> First, technically returning 9 for a test of add(4,5) is correct. Your tests define what the function does, not the name. You are technically correct that te

> First, technically returning 9 for a test of add(4,5) is correct. Your tests define what the function does, not the name. You are technically correct that testing "add(4,5) == 9" is valid. However, everyone already knows that an "add(a,b)" function which always returns 9 is broken. > So when you add the add(10,2) test case, the really pedantic way of doing it would be to handle the extra case with an if-check Saying an if-check is the correct way to refactor does a disservice to TDD practitioners everywhere. Implementing a trivial add function via TDD is just bad. It would have been far better to choose something slightly more complicated such as sorting or fizzbuzz.