Test-Driven Development

Related link: http://www.artima.com/intv/testdriven.html

Artima.com has published Part V of an interview in which Martin Fowler discusses the unhurried quality of test-first design, defines monological thinking, and distinguishes between unit and functional testing.

Here's an excerpt:

The thing I like about taking small steps and writing tests first is that it gives me a simple to do list of the things I've got to do. At each end point I have a certain amount of closure. I say, OK, this stuff works. Check it in. It's all there. It does what it does and it does it correctly.

There's an impossible-to-express quality about test- first design that gives you a sense of unhurriedness. You are actually moving very quickly, but there's an unhurriedness because you are creating little micro-goals for yourself and satisfying them. At each point you know you are doing one micro-goal piece of work, and it's done when the test passes. That is a very calming thing. It reduces the scope of what you have to think about. You don't have to think about everything you have to do in the class. You just have to think about one little piece of responsibility. You make that work and then you refactor it so everything is very nicely designed. Then you add in the next piece of responsibility. I previously used the kind of approach you describe. I'd ask, "What's the interface of this?" I've now switched and I much more prefer incremental design.