I've been developing in and increasing my knowledge of Ruby and RoR for the last few months but I think it's now overdue for me to really get to grips with the built-in testing environment.

I understand the reasons for test driven development and have a basic understanding of how the testing environment in RoR works but I have yet to find a really good resource that covers testing in depth, at least not one aimed at a beginner to tdd. I've been through the testing section of Agile Web Development with Rails but it only seems to touch it lightly and was left wanting more guidance.

Do you have some good books/online resources for testing in RoR? Any tips that you would like to share?