Writing unit tests helps to make sure your application's model and controller code are working properly, but as apps get more and more complex views, it's becoming increasingly important to test the interface of our apps as well. In Xcode 7, Apple introduced a new UI testing feature that allows us to do just that.
When building an app, we have a certain way that our logic is expected to function. Earlier, we expected that by passing an input string to our save function we would get a data representation of a new snippet on disk, so we wrote a test to ensure this was happening. This same idea can be applied to the actual user interface, instead of the logic behind it.
For example, in our app, we want to make sure that when the New button is tapped, the user is presented with an action sheet for them to choose an option from. We could write a unit test to check the button code, but that won't check to make sure that the button event is firing properly...