Helper class for presenting view controllers from context of an Xcode unit testing target.

ViewControllerTestHelper.swift

//
//  Helper class for presenting view controllers from context of an Xcode unit testing target.
//
//  Ported from original Objective-C version at 
//  https://github.com/klaaspieter/KPAViewControllerTestHelper/blob/master/Classes/KPAViewControllerTestHelper.m
//

import Foundation
import UIKit

public class ViewControllerTestHelper {
    
    typealias ContainerViewControllerPresentationBlock = (_ containerViewController: UIViewController, _ viewController: UIViewController) -> Void
    
    static var testHelperWindows: [UIWindow] = [UIWindow]()
    
    @discardableResult
    static func prepareWindowWithRootViewController(rootViewController: UIViewController) -> UIWindow {
        var frame = UIScreen.main.bounds
        frame.origin = CGPoint(x: 0, y: 0)
        let window = UIWindow(frame: frame)
        window.backgroundColor = UIColor.white
        window.makeKeyAndVisible()
        window.rootViewController = rootViewController
        wait()
        testHelperWindows.append(window)
        return window
    }
    
    static func presentViewController(viewController: UIViewController) {
        makeViewControllerVisible(controller: viewController, inContainerViewController: emptyViewController()) { (containerViewController, viewController) -> Void in
            containerViewController.present(viewController, animated: false, completion: nil)
        }
    }
    
    static func pushViewController(viewController: UIViewController) {
        let navigationController = UINavigationController(rootViewController: emptyViewController())
        makeViewControllerVisible(controller: viewController, inContainerViewController: navigationController) { (containerViewController, viewController) -> Void in
            navigationController.pushViewController(viewController, animated: false)
        }
    }
    
    static func dismissViewController(viewController: UIViewController) {
        viewController.dismiss(animated: false, completion: nil)
        wait()
    }
    
    static func presentAndDismissViewController(viewController: UIViewController) {
        presentViewController(viewController: viewController)
        dismissViewController(viewController: viewController)
    }
    
    static func wait() {
        wait(seconds: 0.01)
    }
    
    static func wait(seconds: TimeInterval) {
        RunLoop.main.run(until: NSDate(timeIntervalSinceNow: seconds) as Date)
    }
    
    static func emptyViewController() -> UIViewController {
        let viewController = UIViewController()
        viewController.view = UIView()
        return viewController
    }
    
    static func makeViewControllerVisible(controller: UIViewController, inContainerViewController container: UIViewController, withPresentationBlock presentationBlock: ContainerViewControllerPresentationBlock) {
        prepareWindowWithRootViewController(rootViewController: container)
        presentationBlock(container, controller)
        wait()
    }
    
    static func tearDown() {
        testHelperWindows.forEach { window in
            window.isHidden = true
        }
        wait()
        testHelperWindows = [UIWindow]()
    }
}