One last testing concern worth mentioning is the need to take your app offline and get out of the lab. As developers, it's very easy for us to get totally absorbed in our work and forget that outside of our cubicle there is (literally) an entire world. Real-world variables such as poor cell reception, inaccurate GPS reception, and Wi-Fi dead spots can all cause our applications to behave in unpredictable ways if we don't design for these scenarios. You can simulate the offline mode in your simulator by simply turning off the Wi-Fi to OS X and unplugging any network cables, but Wi-Fi isn't the only variable you need to be concerned about.

Therefore, it is extremely important to take the app out from behind the desk as often as you can. For example, I was recently working with a team on a map-based application. While I was working in the office, everything seemed to be going well. GPS accuracy was exceptional, signal strength was off the chart, and Wi-Fi was constantly...