dispatch_group_leave crash in swift
In the worst case, you can check the discount group's count via its debugDescription String:
let count = self.groupExecuting.debugDescription.components(separatedBy: ",").filter({$0.contains("count")}).first!.components(separatedBy: CharacterSet.decimalDigits.inverted).filter({Int($0) != nil})assert(count.first != "0")This strategy is further explored in this question: DispatchGroup: check how many "entered"