I had some fun learning about JUnit recently. I've always believed that it's important to develop incrementally. The neat thing (to me) about unit testing is that it encourages incremental development -- if you have lots of tests that don't pass, then the natural thing to do is to pick them off, one at a time, and fix them. In grad school, and now as a professor, I've had a fair number of occasions where someone said "I'm almost done writing it up, I should be ready to compile in a day or two". Perhaps encouraging students to develop their tests first will discourage them from falling into that pattern of behavior.
Anyhow, I built a tutorial about JUnit, for use in my CSE398 class. Feel free to share your thoughts on the tutorial, JUnit, and test-driven development in the comments!