Charles' Six Rules of Unit Testing

1. Write the test first
2. Never write a test that succeeds the first time
3. Start with the null case, or something that doesn't work
4. Don't be afraid of doing something trivial to make the test work
5. Loose coupling and testability go hand in hand
6. Use mock objects

from http://radio.weblogs.com/0100190/stories/2002/07/25/sixRulesOfUnitTesting.html