http://junit.sourceforge.net/doc/cookstour/cookstour.htm

This article gives you an insider's view of how JavaUnit '''could have been''' developed. It is extremely pattern-dense, and in a mere 10 pages tells you how to create a unit testing framework, and why each part is built the way it is. It can be tough to read, but once you "get it", you can pretty much write a TestingFramework in any language that has decent modular programming capabilities; I did just this with VbaUnit and LingoUnit.

A great way to learn the ins and outs of a language.
A great way to learn to the ins and outs of a language.