Here it is a flow of random thoughts about Test Driven Development. Naturally IMHO.

• TDD is not about testing application is about design application, and have a (nice) side effect that creates a suite of tests
• The Test obtained with TDD does not cover all the cases, but you can write more test when you need new cases or find a new bug
• The code written in TDD is less and it focused on the needs
• The code written in TDD is more orthogonal and simpler to maintain
• The first red bar is the signal that the test is testing something (and it is very important)
• The tests cannot contains if, switch, etc…so they need to be simple
• Learning TDD is difficult: the impact is the same that you have when passing from structured programming to Object Oriented Programming
• Learning TDD requires times and perseverance
• You cannot learn TDD reading articles and books, you must try it
• Every piece of code is testable
• Testing that the tone of red is that the user likes is not a task of TDD
• With the right use of Mock Objects you can test that the gradient is correctly set
• The test cases comes from the User Stories written with the customer and then they responds to requirements
• The Team that use TDD must be skilled enough…and Pair Programming helps a lot
• The Test code is bigger than the tested code
• TDD force you to think about what you’re writing
• TDD force you to declare what you need before writing something
• TDD put the developer to the client side of his code and so help him to write better interfaces
• TDD helps you to write cleaner and decoupled code
• The Integration Tests helps you to understand how your class interacts with others
• When you need to refactoring your code you can start from tests
• Tests are documentation: read a test is a great help to understand how to use your class
• TDD does not guarantee that you code doesn’t contains bugs
• TDD guarantee that old bug doesn’t come to life again
• The start up cost of TDD is write off during the life of the project
• The TDD reduce a lot the time needed for manual testing
• With TDD the debugger is used like a surgery tool
• TDD helps you to simplify the problem dividing it in small part and every solved part is a small step to the final solution
• Every test case is a single functionality: if one test fail you have only one problem
• If  you have two red test you have two distinct problems
• Every test add a new functionality to the code
• Is difficult to test multi threading applications
• It’s expensive testing the UI, but there are patterns that decrease the UI code (MVP/MVC)
• The integrations test against database help you to know if the database and the queries are ok
• TDD force you to written less encapsulated code to  make it testable
• TDD force you to write independent object and to inject all the dependencies
• Write test after code is not always possible
• TDD is not a silver bullet (but it’s help a lot!)