Testing if UIAlertController has been presented - swift

Question

I have a protocol I use to allow my ViewControllers to present an alert.
import UIKit
struct AlertableAction {
var title: String
var style: UIAlertAction.Style
var result: Bool
}
protocol Alertable {
func presentAlert(title: String?, message: String?, actions: [AlertableAction], completion: ((Bool) -> Void)?)
}
extension Alertable where Self: UIViewController {
func presentAlert(title: String?, message: String?, actions: [AlertableAction], completion: ((Bool) -> Void)?) {
let generator = UIImpactFeedbackGenerator(style: .medium)
generator.impactOccurred()
let alertController = UIAlertController(title: title, message: message, preferredStyle: .alert)
actions.forEach { action in
alertController.addAction(UIAlertAction(title: action.title, style: action.style, handler: { _ in completion?(action.result) }))
}
present(alertController, animated: true, completion: nil)
}
}
I call this something like
#objc private func didTapLogout() {
presentAlert(
title: nil, message: "Are you sure you want to logout?",
actions: [
AlertableAction(title: "No", style: .cancel, result: false),
AlertableAction(title: "Yes", style: .destructive, result: true),
],
completion: { [weak self] result in
guard result else { return }
self?.presenter.logout()
}
)
}
I'd like to write a unit test to assert when this is called, the presented view controller is UIAlertController.
I was trying something like, but it does not pass
func test_renders_alert_controller() {
sut.show()
XCTAssertNotNil(sut.presentedViewController)
}
class MockViewController: UIViewController, Alertable {
var presentViewControllerTarget: UIViewController?
func show() {
presentAlert(title: nil, message: "Are you sure you want to logout?", actions:
[AlertableAction(title: "No", style: .cancel, result: false)],
completion: nil
)
self.presentViewControllerTarget = self.presentedViewController
}
}

Answer 1

You need to wait for the UIAlertController to be fully visible before running your assertion.
Check out XCTWaiter.
Try something like the below:
let nav = UINavigationController.init(rootViewController: sut)
sut.show()
let exp = expectation(description: "Test after 1.5 second wait")
let result = XCTWaiter.wait(for: [exp], timeout: 1.5)
if result == XCTWaiter.Result.timedOut {
XCTAssertNotNil(nav.visibleViewController is UIAlertController)
} else {
XCTFail("Delay interrupted")
}

Answer 2

ViewControllerPresentationSpy avoids slow, flaky unit tests by capturing the information that would be used to present an alert, without actually presenting any alerts. All you need is to create an AlertVerifier, then call whatever presents your alert:
let alertVerifier = AlertVerifier()
sut.show()
alertVerifier.verify(
title: nil,
message: "Are you sure you want to logout?",
animated: true,
presentingViewController: sut,
actions: [
.cancel("No"),
.destructive("Yes"),
]
)
This verify method checks:
That one alert was presented, with animation.
That the presenting view controller was the System Under Test.
The alert title.
The alert message.
The preferred style of UIAlertController.Style (.alert by default)
The titles and styles of each action.
You can invoke each action by name:
try alertVerifier.executeAction(forButton: "Yes")
(Mark the test as throws. The test will fail if there is no button with the given name.)
Try it to see how fast it is compared to the 1.5 second timeout. Also compare how much you can test.