name: mobile-app-testing
description: Comprehensive mobile app testing strategies for iOS and Android. Covers unit tests, UI tests, integration tests, performance testing, and test automation with Detox, Appium, and XCTest.

Mobile App Testing

Overview

Implement comprehensive testing strategies for mobile applications including unit tests, UI tests, integration tests, and performance testing.

When to Use

• Creating reliable mobile applications with test coverage
• Automating UI testing across iOS and Android
• Performance testing and optimization
• Integration testing with backend services
• Regression testing before releases

Instructions

1. React Native Testing with Jest & Detox

// Unit test with Jest
import { calculate } from '../utils/math';

describe('Math utilities', () => {
  test('should add two numbers', () => {
    expect(calculate.add(2, 3)).toBe(5);
  });

  test('should handle negative numbers', () => {
    expect(calculate.add(-2, 3)).toBe(1);
  });
});

// Component unit test
import React from 'react';
import { render, screen } from '@testing-library/react-native';
import { UserProfile } from '../components/UserProfile';

describe('UserProfile Component', () => {
  test('renders user name correctly', () => {
    const mockUser = { id: '1', name: 'John Doe', email: '[email protected]' };
    render(<UserProfile user={mockUser} />);

    expect(screen.getByText('John Doe')).toBeTruthy();
  });

  test('handles missing user gracefully', () => {
    render(<UserProfile user={null} />);
    expect(screen.getByText(/no user data/i)).toBeTruthy();
  });
});

// E2E Testing with Detox
describe('Login Flow E2E Test', () => {
  beforeAll(async () => {
    await device.launchApp();
  });

  beforeEach(async () => {
    await device.reloadReactNative();
  });

  it('should login successfully with valid credentials', async () => {
    await waitFor(element(by.id('emailInput')))
      .toBeVisible()
      .withTimeout(5000);

    await element(by.id('emailInput')).typeText('[email protected]');
    await element(by.id('passwordInput')).typeText('password123');
    await element(by.id('loginButton')).multiTap();

    await waitFor(element(by.text('Home Feed')))
      .toBeVisible()
      .withTimeout(5000);
  });

  it('should show error with invalid credentials', async () => {
    await element(by.id('emailInput')).typeText('[email protected]');
    await element(by.id('passwordInput')).typeText('wrongpass');
    await element(by.id('loginButton')).multiTap();

    await waitFor(element(by.text(/invalid credentials/i)))
      .toBeVisible()
      .withTimeout(5000);
  });

  it('should navigate between tabs', async () => {
    await element(by.id('profileTab')).tap();
    await waitFor(element(by.text('Profile')))
      .toBeVisible()
      .withTimeout(2000);

    await element(by.id('homeTab')).tap();
    await waitFor(element(by.text('Home Feed')))
      .toBeVisible()
      .withTimeout(2000);
  });
});

2. iOS Testing with XCTest

import XCTest
@testable import MyApp

class UserViewModelTests: XCTestCase {
  var viewModel: UserViewModel!
  var mockNetworkService: MockNetworkService!

  override func setUp() {
    super.setUp()
    mockNetworkService = MockNetworkService()
    viewModel = UserViewModel(networkService: mockNetworkService)
  }

  func testFetchUserSuccess() async {
    let expectedUser = User(id: UUID(), name: "John", email: "[email protected]")
    mockNetworkService.mockUser = expectedUser

    await viewModel.fetchUser(id: expectedUser.id)

    XCTAssertEqual(viewModel.user?.name, "John")
    XCTAssertNil(viewModel.errorMessage)
    XCTAssertFalse(viewModel.isLoading)
  }

  func testFetchUserFailure() async {
    mockNetworkService.shouldFail = true

    await viewModel.fetchUser(id: UUID())

    XCTAssertNil(viewModel.user)
    XCTAssertNotNil(viewModel.errorMessage)
    XCTAssertFalse(viewModel.isLoading)
  }
}

class MockNetworkService: NetworkService {
  var mockUser: User?
  var shouldFail = false

  override func fetch<T: Decodable>(
    _: T.Type,
    from endpoint: String
  ) async throws -> T {
    if shouldFail {
      throw NetworkError.unknown
    }
    return mockUser as! T
  }
}

// UI Test
class LoginUITests: XCTestCase {
  override func setUp() {
    super.setUp()
    continueAfterFailure = false
    XCUIApplication().launch()
  }

  func testLoginFlow() {
    let app = XCUIApplication()

    let emailTextField = app.textFields["emailInput"]
    let passwordTextField = app.secureTextFields["passwordInput"]
    let loginButton = app.buttons["loginButton"]

    emailTextField.tap()
    emailTextField.typeText("[email protected]")

    passwordTextField.tap()
    passwordTextField.typeText("password123")

    loginButton.tap()

    let homeText = app.staticTexts["Home Feed"]
    XCTAssertTrue(homeText.waitForExistence(timeout: 5))
  }

  func testNavigationBetweenTabs() {
    let app = XCUIApplication()
    let profileTab = app.tabBars.buttons["Profile"]
    let homeTab = app.tabBars.buttons["Home"]

    profileTab.tap()
    XCTAssertTrue(app.staticTexts["Profile"].exists)

    homeTab.tap()
    XCTAssertTrue(app.staticTexts["Home"].exists)
  }
}

3. Android Testing with Espresso

@RunWith(AndroidJUnit4::class)
class UserViewModelTest {
  private lateinit var viewModel: UserViewModel
  private val mockApiService = mock<ApiService>()

  @Before
  fun setUp() {
    viewModel = UserViewModel(mockApiService)
  }

  @Test
  fun fetchUserSuccess() = runTest {
    val expectedUser = User("1", "John", "[email protected]")
    `when`(mockApiService.getUser("1")).thenReturn(expectedUser)

    viewModel.fetchUser("1")

    assertEquals(expectedUser.name, viewModel.user.value?.name)
    assertEquals(null, viewModel.errorMessage.value)
  }

  @Test
  fun fetchUserFailure() = runTest {
    `when`(mockApiService.getUser("1"))
      .thenThrow(IOException("Network error"))

    viewModel.fetchUser("1")

    assertEquals(null, viewModel.user.value)
    assertNotNull(viewModel.errorMessage.value)
  }
}

// UI Test with Espresso
@RunWith(AndroidJUnit4::class)
class LoginActivityTest {
  @get:Rule
  val activityRule = ActivityScenarioRule(LoginActivity::class.java)

  @Test
  fun testLoginWithValidCredentials() {
    onView(withId(R.id.emailInput))
      .perform(typeText("[email protected]"))

    onView(withId(R.id.passwordInput))
      .perform(typeText("password123"))

    onView(withId(R.id.loginButton))
      .perform(click())

    onView(withText("Home"))
      .check(matches(isDisplayed()))
  }

  @Test
  fun testLoginWithInvalidCredentials() {
    onView(withId(R.id.emailInput))
      .perform(typeText("[email protected]"))

    onView(withId(R.id.passwordInput))
      .perform(typeText("wrongpassword"))

    onView(withId(R.id.loginButton))
      .perform(click())

    onView(withText(containsString("Invalid credentials")))
      .check(matches(isDisplayed()))
  }

  @Test
  fun testNavigationBetweenTabs() {
    onView(withId(R.id.profileTab)).perform(click())
    onView(withText("Profile")).check(matches(isDisplayed()))

    onView(withId(R.id.homeTab)).perform(click())
    onView(withText("Home")).check(matches(isDisplayed()))
  }
}

4. Performance Testing

import XCTest

class PerformanceTests: XCTestCase {
  func testListRenderingPerformance() {
    let viewModel = ItemsViewModel()
    viewModel.items = (0..<1000).map { i in
      Item(id: UUID(), title: "Item \(i)", price: Double(i))
    }

    measure {
      _ = viewModel.items.filter { $0.price > 50 }
    }
  }

  func testNetworkResponseTime() {
    let networkService = NetworkService()

    measure {
      let expectation = XCTestExpectation(description: "Fetch user")

      Task {
        do {
          _ = try await networkService.fetch(User.self, from: "/users/test")
          expectation.fulfill()
        } catch {
          XCTFail("Network request failed")
        }
      }

      wait(for: [expectation], timeout: 10)
    }
  }
}

Best Practices

✅ DO

• Write tests for business logic first
• Use dependency injection for testability
• Mock external API calls
• Test both success and failure paths
• Automate UI testing for critical flows
• Run tests on real devices
• Measure performance on target devices
• Keep tests isolated and independent
• Use meaningful test names
• Maintain >80% code coverage

❌ DON'T

• Skip testing UI-critical flows
• Use hardcoded test data
• Ignore performance regressions
• Test implementation details
• Make tests flaky or unreliable
• Skip testing on actual devices
• Ignore accessibility testing
• Create interdependent tests
• Test without mocking APIs
• Deploy untested code