I note that the book contains a chapter on unittesting and mocking in Groovy. I'm curious about the experiences of the authors and others doing either TDD or simple unit testing with Groovy.
Not only is unit testing important in Groovy, it also helps with it significantly. I think this is also an area that is great on projects to introduced Groovy. You can test Java code and also test Groovy code. You can take advantage of exiting mock framework in Java or take advantage of the mocking capabilities in Groovy. I am a huge fan of TDD and Groovy is a great language for practicing TDD.