11 April 2024 Leave a comment Tech-Help
When developing an app with a user interface, it’s crucial to ensure that navigation between different screens behaves as expected. For developers utilizing XCTest for UI testing in Swift, one common challenge is verifying that a particular view controller is presented after an action such as a button tap.
Understanding UI Testing Limitations
The UI Testing framework in XCTest operates at an arm’s length from the application’s code. This means that it does not have the ability to directly access instances of view controllers to make assertions about their class types. In other words, you cannot straightforwardly assert the class of the currently displayed view controller.
Adopting a User-Centric Testing Approach
Rather than attempting to verify the view controller class, we can adopt a user-centric approach to UI testing. Consider what the user would see and interact with, rather than the underlying code structure. For instance, users identify their current context through visual cues like screen titles, button names, or other static text elements.
Testing Based on Visible UI Elements
Let’s say you have a button that, when tapped, should navigate to a particular screen within a navigation stack. You can assert the presence of the screen by checking for the title:
let app = XCUIApplication()
app.buttons["View Item"].tap()
XCTAssert(app.navigationBars["Some Item"].exists)
Similarly, for modal screens or screens without a navigation bar, look for unique static text or buttons that you expect to be present on the screen:
let app = XCUIApplication()
app.buttons["View Item"].tap()
XCTAssert(app.staticTexts["Item Detail"].exists)
XCTAssert(app.buttons["Remove Item"].exists)
Alternative Method: Accessibility Identifiers
An alternative approach involves using accessibility identifiers to indirectly determine the current view controller. This method requires setting up a unique, unused UI element within a base view controller class, assigning it an accessibility label, and then querying for this label in your tests.
Here’s how you could implement and test using this strategy:
public class BaseViewController: UIViewController {
let button = UIButton(frame: CGRect(x: 0, y: 0, width: 1, height: 1))
public override func viewDidLoad() {
super.viewDidLoad()
if let identifier = self.theClassName.split(separator: ".").last {
button.accessibilityIdentifier = String(identifier)
view.addSubview(button)
}
}
}
public class DatePickerViewController: BaseViewController {
...
}
func testExample() {
let app = XCUIApplication()
app.launch()
app.navigationBars.buttons["DateSelector"].tap()
XCTAssertTrue(app.buttons["DatePickerViewController"].exists)
}
Remember, the UI element you use for identification purposes must be added as a subview with a non-zero frame to be detectable by the testing framework.
Conclusion
While direct class assertions on view controller instances are not possible with XCTest’s UI Testing framework, by thinking like a user and focusing on the visible UI elements, you can effectively verify screen transitions. Whether you assert based on UI titles and elements or utilize accessibility identifiers, both methods provide a robust solution for ensuring your UI navigates as expected during tests.
