One of the most important things of unit testing is that it shouldn’t have side effects. If you don’t pay attention, you may have unexpected behaviours every time you run your set of tests. A fake `AppDelegate` may solve your problems.
A keen developer writes a lot of unit tests to cover the code to use in production. Unfortunately, a component can sometimes be difficult to test because of its dependencies, and you would be tempted to give up. Hang on, Test Doubles are what you need to make a test easy to write.
Are you developing an application which uses API responses? Do you need an efficiently way to test the UI? UI testing with a mock API server is the solution to your problems.