Unit testing ViewModels in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a test class for a ViewModel in Swift.

iOS Swift

class [1]: XCTestCase {
}

Drag options to blanks, or click blank then click option'

AMyViewModelTests

BViewModel

CTestViewModel

DViewModelTestCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic class name like 'ViewModel' without 'Tests'.

Not inheriting from XCTestCase (not shown here but important).

The test class should be named clearly to indicate it tests the ViewModel, commonly ending with Tests.

2fill in blank

medium

Complete the code to create an instance of the ViewModel inside the test class.

iOS Swift

var viewModel: [1]!

override func setUp() {
  super.setUp()
  viewModel = [1]()
}

Drag options to blanks, or click blank then click option'

AViewModelTests

BMyViewModel

CXCTestCase

DTestViewModel

Attempts:

3 left

💡 Hint

Common Mistakes

Using the test class name instead of the ViewModel class.

Not initializing the ViewModel in setUp.

The ViewModel instance should be of the actual ViewModel class, here named MyViewModel.

3fill in blank

hard

Fix the error in the test method to check if the ViewModel's title is correct.

iOS Swift

func testTitle() {
  let expected = "Welcome"
  XCTAssertEqual(viewModel.[1], expected)
}

Drag options to blanks, or click blank then click option'

AtitleText

Btitle()

CgetTitle()

Dtitle

Attempts:

3 left

💡 Hint

Common Mistakes

Using method call syntax for a property.

Using a wrong property name.

The property to test is usually named title without parentheses if it is a property, not a method.

4fill in blank

hard

Fill both blanks to test if the ViewModel updates its count correctly after increment.

iOS Swift

func testIncrement() {
  viewModel.increment()
  XCTAssertEqual(viewModel.[1], [2])
}

Drag options to blanks, or click blank then click option'

Acount

B1

C0

Dincrement

Attempts:

3 left

💡 Hint

Common Mistakes

Checking the wrong property.

Expecting the count to be 0 after increment.

The test checks if the count property equals 1 after calling increment().

5fill in blank

hard

Fill all three blanks to test if the ViewModel filters items correctly.

iOS Swift

func testFilterItems() {
  let filtered = viewModel.items.filter { $0.[1].[2]([3]) }
  XCTAssertEqual(filtered.count, 2)
}

Drag options to blanks, or click blank then click option'

Aname

Bcontains

C"a"

DisEmpty

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'isEmpty' instead of 'contains'.

Filtering on the wrong property.

The test filters items whose name contains the letter "a".

Practice

1. What is the main purpose of unit testing a ViewModel in iOS development?

easy

A. To verify the app's business logic without involving the user interface

B. To test the app's user interface elements visually

C. To check the app's network connectivity

D. To measure the app's performance speed

Solution

1. Step 1: Understand the role of ViewModel

   The ViewModel handles app logic and data preparation, separate from UI.

2. Step 2: Identify unit testing focus

   Unit testing targets logic correctness without UI involvement.

3. Final Answer:

   To verify the app's business logic without involving the user interface -> Option A

4. Quick Check:

   Unit testing ViewModel = test logic only [OK]

Hint: Unit tests check logic, not UI or performance [OK]

Common Mistakes:

• Confusing unit tests with UI tests
• Thinking unit tests check network or performance
• Assuming ViewModel tests require UI elements

2. Which XCTest method is used to prepare the environment before each test runs in a ViewModel test class?

easy

A. setUp()

B. runTest()

C. testExample()

D. tearDown()

Solution

1. Step 1: Recall XCTest lifecycle methods

   setUp() runs before each test to prepare needed objects.

2. Step 2: Differentiate from tearDown()

   tearDown() cleans up after each test, not before.

3. Final Answer:

   setUp() -> Option A

4. Quick Check:

   Prepare tests before running = setUp() [OK]

Hint: setUp() runs before each test to prepare environment [OK]

Common Mistakes:

• Using tearDown() to prepare tests instead of clean up
• Confusing testExample() as a setup method
• Assuming runTest() is a XCTest lifecycle method

3. Given this ViewModel test code snippet, what will be the value of result after the test runs?

class CounterViewModel {
  var count = 0
  func increment() { count += 1 }
}

func testIncrement() {
  let vm = CounterViewModel()
  vm.increment()
  let result = vm.count
}

medium

A. Compilation error

B. 0

C. nil

D. 1

Solution

1. Step 1: Analyze initial state

   CounterViewModel starts with count = 0.

2. Step 2: Apply increment method

   increment() adds 1 to count, so count becomes 1.

3. Final Answer:

   1 -> Option D

4. Quick Check:

   Increment once = count 1 [OK]

Hint: Increment adds 1, so count becomes 1 [OK]

Common Mistakes:

• Assuming count stays 0 without increment
• Thinking result is nil because of missing return
• Expecting compilation error due to missing test annotation

4. Identify the error in this ViewModel unit test code:

class MyViewModel {
  var value = 0
  func updateValue() { value = 10 }
}

func testUpdateValue() {
  let vm = MyViewModel()
  vm.updateValue()
  XCTAssertEqual(vm.value, 0)
}

medium

A. updateValue() method is missing return type

B. XCTAssertEqual expects 10 but checks for 0

C. MyViewModel class is not marked as final

D. vm instance is not initialized properly

Solution

1. Step 1: Check updateValue() effect

   updateValue() sets value to 10, so vm.value should be 10.

2. Step 2: Compare XCTAssertEqual parameters

   Test expects vm.value to be 0, which is incorrect after updateValue().

3. Final Answer:

   XCTAssertEqual expects 10 but checks for 0 -> Option B

4. Quick Check:

   Test expected value must match updated value [OK]

Hint: Check expected vs actual values in XCTAssertEqual [OK]

Common Mistakes:

• Ignoring the expected value in XCTAssertEqual
• Thinking missing return type causes error here
• Assuming class must be final for testing

5. You want to test a ViewModel method that fetches user data asynchronously and updates a userName property. Which approach correctly tests this behavior using XCTest?

hard

A. Call the method, then immediately assert userName without waiting

B. Test only synchronous methods; skip async ones

C. Use XCTestExpectation to wait for the async update before asserting userName

D. Mock the ViewModel and do not call the real method

Solution

1. Step 1: Understand async testing need

   Async methods update properties after delay, so test must wait.

2. Step 2: Use XCTestExpectation

   Expectation waits for async completion before asserting userName value.

3. Final Answer:

   Use XCTestExpectation to wait for the async update before asserting userName -> Option C

4. Quick Check:

   Async test = use XCTestExpectation [OK]

Hint: Wait for async calls with XCTestExpectation before assertions [OK]

Common Mistakes:

• Asserting async results immediately without waiting
• Skipping async tests thinking they are too complex
• Mocking ViewModel without testing real async behavior