Swift Testing

You are a Swift testing specialist. The user wants to write XCTest unit and UI tests for iOS apps.

What to check first

• Run xcodebuild -showsdks to verify iOS SDK is installed
• Open your .xcodeproj and confirm a test target exists (or create one via File → New → Target → Unit Testing Bundle)
• Check Product → Scheme → Edit Scheme and ensure Test phase is configured with your test target

Steps

1. Create a test file by right-clicking your test target in Xcode, selecting "New File," and choosing "Unit Test Case Class"
2. Import XCTest at the top: import XCTest and @testable import YourAppName to access internal classes
3. Subclass XCTestCase and write test methods prefixed with test (e.g., func testLoginValidation())
4. Use XCTAssertEqual(_:_:), XCTAssertTrue(_:), and XCTAssertNil(_:) to validate expected outcomes
5. For async code, use expectation(description:) and waitForExpectations(timeout:handler:) to handle completion handlers
6. Create UI tests by adding a UI Testing Bundle target, then write tests using XCUIApplication() to launch and interact with the app
7. Use XCUIApplication().buttons["LoginButton"].tap() and XCUIApplication().textFields.element.typeText("user@example.com") for UI interactions
8. Run tests with Cmd+U or xcodebuild test -scheme YourScheme -destination 'platform=iOS Simulator,name=iPhone 15'

Code

import XCTest
@testable import MyApp

final class LoginViewModelTests: XCTestCase {
    var viewModel: LoginViewModel!
    
    override func setUp() {
        super.setUp()
        viewModel = LoginViewModel()
    }
    
    override func tearDown() {
        viewModel = nil
        super.tearDown()
    }
    
    func testEmailValidation() {
        let isValid = viewModel.isValidEmail("test@example.com")
        XCTAssertTrue(isValid)
    }
    
    func testInvalidEmailValidation() {
        let isValid = viewModel.isValidEmail("invalid-email")
        XCTAssertFalse(isValid)
    }
    
    func testLoginSuccess() {
        let expectation = expectation(description: "Login completes")
        
        viewModel.login(email: "test@example.com", password: "password123") { result in
            switch result {
            case .success(let user):
                XCTAssertEqual(user.id, "123")
                expectation.fulfill()
            case .failure:
                XCTFail("Login should succeed")
            }
        }

Note: this example was truncated in the source. See the GitHub repo for the latest full version.

Common Pitfalls

• Treating this skill as a one-shot solution — most workflows need iteration and verification
• Skipping the verification steps — you don't know it worked until you measure
• Applying this skill without understanding the underlying problem — read the related docs first

When NOT to Use This Skill

• When a simpler manual approach would take less than 10 minutes
• On critical production systems without testing in staging first
• When you don't have permission or authorization to make these changes

How to Verify It Worked

• Run the verification steps documented above
• Compare the output against your expected baseline
• Check logs for any warnings or errors — silent failures are the worst kind

Production Considerations

• Test in staging before deploying to production
• Have a rollback plan — every change should be reversible
• Monitor the affected systems for at least 24 hours after the change