A common argument against writing automated unit tests is that no one has time to write them. Ultimately this is not true, in that writing code with unit tests takes no longer than writing code without them.
Without unit tests devs still need to assert that their code works. This typically means writing the code, then launching the application and ensuring the code does what it’s supposed to do. This is then repeated as you continue to implement functionality. Unit testing is written using the time they would normally spend running the application to assert that the code works. The real difference appears when you start looking at continuous revision. As you revise code, are you always going back over the complete functionality to ensure your new code hasn’t broken any previously verified behaviour? Honestly, you should be, but think how much time that would take.
As you begin to invest pieces of time writing unit tests instead of manually firing up applications to one-time test, you are still asserting your code will do what you expect it to do, and you gain that regression assessment for free.
For the record, my acronym for testing style would be BDTSD. (Behaviour Driven Test Soon Development:)