TDD *is to* about testing

It's very much in vogue at the moment to talk about TDD, and to mention, knowingly, and in passing that "of course, TDD is not about testing, it's about X". X is behaviour, design, specification and any number of other things.

Bollocks

Test-Driven Development is a combination of test-first programming and refactoring. There are a great many advantages to using tests to drive your development, and a simpler, cleaner design is one of them. A cleaner understanding of the behaviour you require before you start to implement it is another. An "executable specification" is yet another way to think about what you're doing.

All of these effects are Good Things, but one major advantage of TDD is the ability to answer the question "how will I know I am done?". We can aswer that question because we have a test that will fail if we are not done and pass if we are.

Test-Driven Development is about testing (at least it is the way I do it). What needs to be more explicitly stated and articulated is that it's not JUST about testing.