iOS Testing Skill

Build reliable iOS apps with comprehensive testing

Learning Objectives

By completing this skill, you will:

• Write effective unit tests with XCTest
• Create reliable UI tests
• Implement proper mocking strategies
• Debug efficiently with Instruments
• Achieve high code coverage

Prerequisites

Curriculum

Module 1: XCTest Fundamentals (4 hours)

Topics:

• XCTestCase structure
• Assertions library
• Test lifecycle (setUp/tearDown)
• Async testing

Code Example:

final class UserViewModelTests: XCTestCase {
    private var sut: UserViewModel!
    private var mockService: MockUserService!

    override func setUp() {
        super.setUp()
        mockService = MockUserService()
        sut = UserViewModel(service: mockService)
    }

    func test_loadUser_success() async {
        mockService.result = .success(.mock())

        await sut.loadUser(id: "123")

        XCTAssertNotNil(sut.user)
        XCTAssertFalse(sut.isLoading)
    }
}

Module 2: Mocking & Test Doubles (4 hours)

Topics:

• Protocol-based mocking
• Spy, stub, fake patterns
• Dependency injection for testing
• Fixtures and factories

Module 3: UI Testing (5 hours)

Topics:

• XCUIApplication setup
• Element queries
• Accessibility identifiers
• Page Object pattern
• Handling flaky tests

Module 4: Debugging (4 hours)

Topics:

• LLDB commands
• Breakpoints (symbolic, conditional)
• View Debugger
• Memory Graph Debugger

Module 5: Performance Testing (3 hours)

Topics:

• XCTMetric usage
• Time Profiler
• Allocations instrument
• Leaks detection

Module 6: CI Integration (3 hours)

Topics:

• Xcode Cloud setup
• GitHub Actions
• Code coverage reports
• Test parallelization

Assessment Criteria

Coverage Targets

Common Mistakes

1. Testing implementation → Test behavior instead
2. Flaky UI tests → Use waitForExistence
3. Missing tearDown → Clean up resources
4. Slow tests → Use mocks, avoid network

Skill Validation

1. Test Suite: 80% coverage on sample project
2. Mock Library: Reusable mock implementations
3. UI Test Flow: End-to-end login flow
4. Performance Baseline: Measure scroll performance