AsynchronousTestingCorrectly.swift

class AsynchronousTesting: XCTestCase {
    var clientManager: APIManager!
    
    func setUp() {
        clientManager = APIManager()
    }

    func testLongOperationCorrectly() {
        var users: [Users] = []
        let fetchExpectation = expectationWithDescription("Fetching list of users")
        clientManager.getListOfUsers { incomingUsers, error in
            if error == nil {
                users = incomingUsers
                XCTAssert(users.count > 0, "Users returned should always be greater than zero")
                fetchExpectation.fulfill()
            }        
        }
        
        waitForExpectationsWithTimeout(5, handler: nil)
    }
}