Before submitting to the App Store, it is a good idea to test the App once again precisely. I tend to install my App on a device and give it a friend for a while. Then I tak
Two major points:
Use unit testing. You can use Google Toolbox for Mac for that or just roll your own.
User testing, well, it's user testing. A colleague of mine designed a 50-point walkthrough/questionnaire of the app and had some 10-20 people do it -- and then repeated certain parts when we made changes to certain sections.