runtime_stubbing.swift

//Example of a runtime check stubbing
class User {
    
}

enum ResultType<T> {
    case success(T)
    case error(Error)
}

class DAO {
    
    enum Source {
        case server
        case stubbed
    }
    
    var source: Source
    
    init(source: Source = Source.server ) {
        self.source = source
    }
}

class UserDAO: DAO {
    
    func getAll(completion: @escaping (ResultType<[User]>) -> Void) {
        if source == .server {
            print("Real data from the server")
        } else {
            print("Stubbed data from the mocks")
        }
    }
}
//In the tests
let daoTest: UserDAO = UserDAO(source: DAO.Source.stubbed)
print("Test")
daoTest.getAll(completion: { _ in })

//On the app
let dao: UserDAO = UserDAO()
print("APP")
dao.getAll(completion: { _ in })

//Output 
//Test
//Stubbed data from the mocks
//APP
//Real data from the server