Testability Is Another Hallmark

There's diminishing returns on the amount of time you can spend defining those tests, and you will never have enough tests to have a full complex system emerge. There is actually one place where i agree that t d d's a good idea - fixing bugs. Before you fix a bug, you should add a unit test that triggers the bug, make unit test fails, then fix the bug and make sure unit test passes. Because otherwise you run the risk t t you haven't actually fixed the bug 100 %.