Mock objects and protocols in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a protocol named Logger with a log function.

iOS Swift

protocol Logger {
    func [1](message: String)
}

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

Awrite

Bprint

Csend

Dlog

Attempts:

3 left

💡 Hint

Common Mistakes

Using a function name that does not describe logging, like 'print' or 'send'.

The protocol requires a function named 'log' to handle logging messages.

2fill in blank

medium

Complete the code to create a mock class MockLogger that conforms to Logger protocol.

iOS Swift

class MockLogger: Logger {
    var messages: [String] = []
    func [1](message: String) {
        messages.append(message)
    }
}

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

Asend

Bprint

Clog

Dwrite

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name than the protocol requires.

The mock class must implement the 'log' function to conform to the Logger protocol.

3fill in blank

hard

Fix the error in the test function to verify the mock logger recorded the message.

iOS Swift

func testLogging() {
    let mockLogger = MockLogger()
    mockLogger.log(message: "Test message")
    assert(mockLogger.[1].count == 1)
}

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

Amessages

BlogMessages

Clogs

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a property name that does not exist in MockLogger.

The mock logger stores logged messages in the 'messages' array.

4fill in blank

hard

Fill both blanks to create a protocol and a mock class that counts calls.

iOS Swift

protocol [1] {
    func fetchData()
}

class MockFetcher: [2] {
    var callCount = 0
    func fetchData() {
        callCount += 1
    }
}

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

ADataFetcher

BLogger

CDataFetcher

DLogger

Attempts:

3 left

💡 Hint

Common Mistakes

Using mismatched protocol and class names.

The protocol is named DataFetcher and the mock class conforms to it to count calls.

5fill in blank

hard

Fill all three blanks to define a protocol, a mock class, and a test verifying call count.

iOS Swift

protocol [1] {
    func save(data: String)
}

class MockSaver: [2] {
    var saveCalls = 0
    func save(data: String) {
        saveCalls += 1
    }
}

func testSave() {
    let mock = MockSaver()
    mock.save(data: "Hello")
    assert(mock.[3] == 1)
}

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

ASaver

BMockSaver

CsaveCalls

DSaver

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect protocol or property names in the test.

The protocol is Saver, the mock class conforms to Saver, and the test checks saveCalls count.

Practice

1. What is the main purpose of a mock object in Swift testing?

easy

A. To improve app performance in production

B. To simulate real objects for testing without using actual implementations

C. To create user interface elements dynamically

D. To store user data securely

Solution

1. Step 1: Understand the role of mock objects

   Mock objects are used to imitate real objects during testing to isolate code behavior.

2. Step 2: Identify the purpose in testing context

   They help test code without relying on real implementations that may be complex or unavailable.

3. Final Answer:

   To simulate real objects for testing without using actual implementations -> Option B

4. Quick Check:

   Mock objects = simulate real objects [OK]

Hint: Mocks imitate real parts only for testing [OK]

Common Mistakes:

• Confusing mocks with production code
• Thinking mocks improve app speed
• Using mocks for UI creation

2. Which of the following is the correct way to declare a protocol in Swift?

easy

A. interface MyProtocol { func doSomething() }

B. class MyProtocol { func doSomething() }

C. protocol MyProtocol { func doSomething() }

D. struct MyProtocol { func doSomething() }

Solution

1. Step 1: Recall Swift syntax for protocols

   Protocols in Swift are declared using the keyword protocol.

2. Step 2: Compare options

   protocol MyProtocol { func doSomething() } uses protocol keyword correctly; others use class, struct, or interface which are incorrect for protocols.

3. Final Answer:

   protocol MyProtocol { func doSomething() } -> Option C

4. Quick Check:

   Swift protocol declaration = protocol keyword [OK]

Hint: Protocols start with the keyword 'protocol' [OK]

Common Mistakes:

• Using class or struct instead of protocol
• Using 'interface' which is not Swift syntax
• Missing the protocol keyword

3. Given the protocol and mock class below, what will be printed when calling mock.fetchData()?

protocol DataFetcher {
  func fetchData() -> String
}

class MockFetcher: DataFetcher {
  func fetchData() -> String {
    return "Mock Data"
  }
}

let mock = MockFetcher()
print(mock.fetchData())

medium

A. "Real Data"

B. Runtime crash

C. Compilation error

D. "Mock Data"

Solution

1. Step 1: Analyze the protocol and mock class

   The protocol requires a method fetchData() returning a String. The mock class implements it returning "Mock Data".

2. Step 2: Check the print statement output

   Calling mock.fetchData() returns "Mock Data", so that is printed.

3. Final Answer:

   "Mock Data" -> Option D

4. Quick Check:

   Mock method returns "Mock Data" [OK]

Hint: Mock returns its own defined value, not real data [OK]

Common Mistakes:

• Assuming it returns 'Real Data'
• Expecting a compile error due to protocol
• Thinking it crashes at runtime

4. What is wrong with the following mock class implementation?

protocol Service {
  func execute() -> Bool
}

class MockService: Service {
  func execute() {
    print("Executed")
  }
}

medium

A. The mock class does not implement the protocol method signature correctly

B. The mock class should be a struct, not a class

C. The protocol cannot be implemented by a class

D. The method should return Void, not Bool

Solution

1. Step 1: Compare protocol method signature with mock method

   The protocol requires execute() to return a Bool, but the mock method returns Void.

2. Step 2: Identify the mismatch causing error

   This mismatch causes a compile error because the mock does not conform properly.

3. Final Answer:

   The mock class does not implement the protocol method signature correctly -> Option A

4. Quick Check:

   Method signature mismatch = error [OK]

Hint: Method signatures must match exactly in mocks [OK]

Common Mistakes:

• Ignoring return type mismatch
• Thinking class vs struct matters here
• Believing protocols can't be implemented by classes

5. You want to test a view controller that depends on a network service. Which approach correctly uses a mock object and protocol to isolate the test?

protocol NetworkService {
  func fetchData(completion: (String) -> Void)
}

class MockNetworkService: NetworkService {
  func fetchData(completion: (String) -> Void) {
    completion("Test Data")
  }
}

// In test:
let mockService = MockNetworkService()
let viewController = MyViewController(service: mockService)
viewController.loadData()

What is the benefit of this setup?

hard

A. It allows testing the view controller without real network calls

B. It speeds up the real network requests

C. It automatically updates the UI without code

D. It stores data permanently on the device

Solution

1. Step 1: Understand the use of protocol and mock

   The protocol defines the network service interface. The mock provides test data without real network calls.

2. Step 2: Identify the testing benefit

   This setup isolates the view controller from real network dependencies, making tests reliable and fast.

3. Final Answer:

   It allows testing the view controller without real network calls -> Option A

4. Quick Check:

   Mock isolates tests from real network [OK]

Hint: Mocks avoid real network calls in tests [OK]

Common Mistakes:

• Thinking mocks speed up real network
• Assuming UI updates automatically
• Confusing mocks with data storage