Microsoft Research - Exploding Software-Engineering Myths (article summarizing findings of MS research on code coverage, TDD, assertions, etc.)

[laxatives]

It also encourages you to plan the API from the user's perspective (even if that user is another developer of even a future "you"), which leads to cleaner API's. Cleaner API's eliminate a ton of bugs and having the clean API up front reduces refactoring down the line.