Snapshot testing in iOS Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is snapshot testing in iOS development?

Snapshot testing is a way to check if the visual appearance of a UI component stays the same over time by comparing its current look to a saved image.

beginner

Which framework is commonly used for snapshot testing in Swift?

The iOSSnapshotTestCase framework (also known as FBSnapshotTestCase) is commonly used for snapshot testing in Swift projects.

intermediate

Why is snapshot testing useful compared to manual UI checks?

Snapshot testing automates UI verification, catching visual bugs quickly and consistently without needing a person to look at the screen every time.

intermediate

What should you do if a snapshot test fails because the UI intentionally changed?

You should update the saved snapshot image to the new correct UI appearance to keep tests accurate.

advanced

Name one limitation of snapshot testing.

Snapshot testing can be fragile if small UI changes happen often, and it may not catch functional bugs that don't affect appearance.

What does a snapshot test compare?

A User input vs validation rules

B Code logic vs expected output

C Network response vs cached data

D Current UI image vs saved UI image

Snapshot tests compare the current UI image to a previously saved image to detect visual changes.

Which of these is a popular snapshot testing framework for Swift?

A XCTest

B iOSSnapshotTestCase

C Alamofire

D CoreData

iOSSnapshotTestCase is a popular framework specifically for snapshot testing in Swift.

If a UI change is intentional, what should you do with the snapshot test?

A Delete the test

B Ignore the failure

C Update the saved snapshot

D Revert the UI change

You should update the saved snapshot to reflect the new correct UI.

Snapshot testing is best described as:

A Testing UI appearance

B Testing app performance

C Testing backend APIs

D Testing user input validation

Snapshot testing focuses on verifying the UI appearance.

One limitation of snapshot testing is:

A It may fail often with small UI changes

B It requires manual UI checks

C It cannot detect visual bugs

D It tests only backend logic

Snapshot tests can be fragile and fail often if the UI changes frequently.

Explain how snapshot testing helps maintain UI quality in iOS apps.

Think about how comparing images can catch bugs without manual review.

Describe the steps to update a snapshot test after a UI change.

Consider what happens when the UI changes on purpose.

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