Roy Osherove book on "The art of unit testing"

Just found out from Roy Osherove's blog that his book on "The Art of Unit Testing" is available for purchasing online -- well, the first 5 chapters are, but then you get the next as they're being published. Roy uses NUnit to illustrate unit testing concepts and techniques, but that shouldn't deter you from buying the book, because the principles are pretty much the same in all languages. I'm a long time reader of Roy's blog and I can say this is good stuff, judging by his past posts on unit testing and mock testing techniques.