Snapshot testing in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a snapshot test for a UIView named myView.

iOS Swift

func testMyViewSnapshot() {
  let myView = UIView()
  // Configure myView
  assertSnapshot(matching: myView, as: .[1])
}

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

Ajson

Btext

Cimage

Daudio

Attempts:

3 left

💡 Hint

Common Mistakes

Using text or json instead of image for UI snapshots.

The snapshot test compares the view's rendered image. Use image as the snapshot format.

2fill in blank

medium

Complete the code to set a fixed size for the view before snapshot testing.

iOS Swift

func testFixedSizeViewSnapshot() {
  let view = UIView(frame: CGRect(x: 0, y: 0, width: [1], height: 100))
  assertSnapshot(matching: view, as: .image)
}

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

A200

B50

C0

D-100

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero or negative width causing empty snapshots.

Setting width to 200 gives the view a visible size for snapshot testing.

3fill in blank

hard

Fix the error in the snapshot test by completing the missing parameter for the snapshot strategy.

iOS Swift

func testLabelSnapshot() {
  let label = UILabel()
  label.text = "Hello"
  assertSnapshot(matching: label, as: .[1])
}

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

Atext

Bjson

Caudio

Dimage

Attempts:

3 left

💡 Hint

Common Mistakes

Using text or json instead of image for UILabel snapshots.

Labels are snapshot tested as images to capture their visual appearance.

4fill in blank

hard

Fill both blanks to create a snapshot test that waits for the view to layout before capturing.

iOS Swift

func testLayoutSnapshot() {
  let view = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
  view.setNeedsLayout()
  view.layoutIfNeeded()
  assertSnapshot(matching: view, as: .[1](precision: [2]))
}

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

Aimage

Btext

C0.99

D1.5

Attempts:

3 left

💡 Hint

Common Mistakes

Using text snapshot or wrong precision values.

Use image snapshot with a precision of 0.99 for slight rendering differences tolerance.

5fill in blank

hard

Fill all three blanks to create a snapshot test for a UIButton with a specific trait and size.

iOS Swift

func testButtonSnapshot() {
  let button = UIButton(type: .system)
  button.setTitle("Tap", for: .normal)
  button.frame = CGRect(x: 0, y: 0, width: [1], height: [2])
  assertSnapshot(matching: button, as: .[3])
}

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

A100

B44

Cimage

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using text snapshot or wrong button sizes.

Set button width to 100, height to 44 (standard height), and snapshot as image.

Practice

1. What is the main purpose of snapshot testing in iOS development?

easy

A. To save a picture of the UI and detect visual changes automatically

B. To test the app's network requests

C. To check the app's memory usage

D. To verify the app's database schema

Solution

1. Step 1: Understand snapshot testing concept

   Snapshot testing captures the UI appearance as an image to compare later.

2. Step 2: Identify the main goal

   The goal is to detect unintended visual changes early by comparing snapshots.

3. Final Answer:

   To save a picture of the UI and detect visual changes automatically -> Option A

4. Quick Check:

   Snapshot testing = UI visual comparison [OK]

Hint: Snapshot testing checks UI images for changes [OK]

Common Mistakes:

• Confusing snapshot testing with network or performance tests
• Thinking it tests app logic instead of UI appearance

2. Which of the following is the correct syntax to assert a snapshot of a SwiftUI view named MyView() using the SnapshotTesting library?

easy

A. assertSnapshot(view: MyView(), as: .text)

B. assertSnapshot(view: MyView(), type: .image)

C. assertSnapshot(MyView(), format: .image)

D. assertSnapshot(matching: MyView(), as: .image)

Solution

1. Step 1: Recall correct function signature

   The SnapshotTesting library uses assertSnapshot(matching:as:) to compare views.

2. Step 2: Match parameters

   Correct usage is assertSnapshot(matching: MyView(), as: .image) to capture image snapshot.

3. Final Answer:

   assertSnapshot(matching: MyView(), as: .image) -> Option D

4. Quick Check:

   assertSnapshot(matching: view, as: .image) [OK]

Hint: Use assertSnapshot(matching: view, as: .image) [OK]

Common Mistakes:

• Using wrong parameter labels like view: or format:
• Using .text instead of .image for UI snapshots

3. Given this SwiftUI snapshot test code snippet:

let view = Text("Hello")
assertSnapshot(matching: view, as: .image)

What will happen if the UI of Text("Hello") changes color from black to red but the snapshot is not updated?

medium

A. The test will fail because the new UI image differs from the saved snapshot

B. The test will pass because text content is the same

C. The test will crash due to color mismatch

D. The test will ignore color changes and pass

Solution

1. Step 1: Understand snapshot comparison

   Snapshot testing compares saved UI images pixel by pixel.

2. Step 2: Effect of UI color change

   Changing text color changes the image, so it no longer matches saved snapshot.

3. Final Answer:

   The test will fail because the new UI image differs from the saved snapshot -> Option A

4. Quick Check:

   UI image change = test failure [OK]

Hint: Any UI visual change causes snapshot test failure [OK]

Common Mistakes:

• Assuming content text match is enough to pass
• Thinking snapshot tests ignore color or style changes

4. You wrote this snapshot test:

assertSnapshot(matching: MyView(), as: .image)

But the test always fails with an error saying the snapshot file is missing. What is the most likely cause?

medium

A. The view MyView() is not a valid SwiftUI view

B. You forgot to record the initial snapshot before running tests

C. The assertSnapshot function is deprecated

D. The test target does not import XCTest

Solution

1. Step 1: Understand snapshot test workflow

   Snapshot tests require recording a snapshot image first to compare against.

2. Step 2: Identify missing snapshot cause

   If snapshot file is missing, it means initial snapshot was not recorded with record=true.

3. Final Answer:

   You forgot to record the initial snapshot before running tests -> Option B

4. Quick Check:

   Missing snapshot file = forgot record step [OK]

Hint: Record snapshot once before testing to avoid missing file errors [OK]

Common Mistakes:

• Assuming test fails due to view code errors
• Not knowing you must record snapshots first

5. You want to test your SwiftUI view ProfileView() on both iPhone 14 and iPad Pro screen sizes using snapshot testing. Which approach correctly tests both devices in one test function?

hard

A. Use assertSnapshot once without specifying device traits

B. Write separate test functions for each device without looping

C. Use a loop over devices and call assertSnapshot with different traits for each device

D. Test only on iPhone 14 because iPad Pro is not supported

Solution

1. Step 1: Understand device traits in snapshot testing

   You can specify device traits like size and scale to simulate different devices.

2. Step 2: Use loop to test multiple devices

   Looping over device traits and calling assertSnapshot for each covers multiple devices in one test.

3. Final Answer:

   Use a loop over devices and call assertSnapshot with different traits for each device -> Option C

4. Quick Check:

   Loop + traits = multi-device snapshot test [OK]

Hint: Loop devices with traits to test multiple screens [OK]

Common Mistakes:

• Testing only one device and missing others
• Not using traits to simulate device sizes
• Writing many separate test functions unnecessarily