You probably want to learn more about TDD and iOS. For example, we haven't discussed how to use TDD in an app using Core Data.
There are many blogs and screencasts on the internet about TDD and iOS (for example, http://qualitycoding.org, http://iosunittesting.com and http://masilotti.com). With the experience you have gained by reading through this book, you now have a good foundation of how to follow these articles and find your own testing style.
Maybe, by learning more about testing in iOS, you might start a blog to share what you have learned. I'm looking forward to reading about your experiments and findings. Let me know where I can find it. You can find me on Twitter at @dasdom.