Exactly. I think most of the TDD probably come to some tutorials which test addition a+b of that sort and demonstrate how to test "ah there's logical error! how

Exactly. I think most of the TDD probably come to some tutorials which test addition a+b of that sort and demonstrate how to test "ah there's logical error! how incredible TDD helps us to identify error early on!". I do some TDD from time to time, but outside of my textbook algorithm, writing pure unit test which involves using mocks is really tough and time-consuming (unless someone has built a test driver for you to use throughout the whole development). In any, if you ever do curl http://localhost:port/mynewapp/page1 http://localhost:port/mynewapp/page1 that's already testing and is doing functional testing. If you write that down before you start writing a piece of code, you are doing TDD to test whether your app will return 200 or not.