[tedyoung]

This is why I love TDD: the only code I need to think about are the tests that implement my expectations. Writing the code itself is easy, I just have to write the dumbest thing that will make the tests pass.

Of course, this all assumes you've got the right architecture for the job.

[gbog]

You're to handle data structures? If you do it wrong, if each bookstore address is duplicated beside the book's entry, tests will pass but you will have migration nightmare very soon.

What you are forgetting here is the essential refactoring step in the loop.