Here is a small presentation that I've made about two weeks ago for our Wire team that provides some overview of Sync Engine testing (by Sync Engine we call our in-house framework that does all networking and data base management). It covers main problems we have to solve and what we still have to do and how we plan to do it. If you want dive deep in code and know i.e. how we deal with Core Data in our tests - checkout this great article for objc.io by Daniel Eggert.