Testing If A View Controller Got Pushed

I want to write a unit test that tests if a view controller is pushed onto the navigation stack. Here is the solution I came up with:

//
func testViewControllerGotPushedStoryboardVersion() {
    class MockNavigationController: UINavigationController {
        var pushedViewController: UIViewController?
        private override func pushViewController(viewController: UIViewController, animated: Bool) {
            pushedViewController = viewController
            super.pushViewController(viewController, animated: animated)
        }
    }
    
    let viewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewControllerWithIdentifier("MasterViewController") as MasterViewController
    
    let mockNavigationController = MockNavigationController(rootViewController: viewController)
    
    let expectation = expectationWithDescription("should push")
    viewController.performSegueWithIdentifier("showDetail", sender: nil)
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, Int64(NSEC_PER_SEC*0)), dispatch_get_main_queue()) { () -> Void in
        XCTAssertTrue(mockNavigationController.pushedViewController is DetailViewController, "")
        expectation.fulfill()
    }
    
    waitForExpectationsWithTimeout(1, handler: nil)
}

What do you think? Is there a better way to test this?