Unit-Testing is an important tool to validate the functionality. But I feel that it is not used to its full potential. Usually developers just test out the functions which takes in some arguments and returns some data model. Although such tests are usefull but they can’t help you to ascertain that the feature would definitely work if the tests are successfull.

CardsStack is an open source library which makes your UICollectionView to awesome set of cards using UICollectionViewLayout.

The common concurrency issues faced are the one related to acessing and modifying the shared resource from different threads. One can think of this as a producer-consumer problem.