We have come a long way in a short time. We’ve got an app that can send tweets and show our Twitter web page. We now have a stable app that isn’t going to crash on us, right?
Well, how do we know that? We have run the app a few times, but have we really pushed the limits of the app? Have we really tried everything that anyone could possibly do to our app? How do we prove that our app is not going to crash before we ship it off to Apple?
And as we start adding features, what proves that those changes work, or that they’re not going to have weird side effects that break the stuff that had been working?
The way we deal with this is to use unit tests.