📸 Snapshot Testing in iOS – Team Notes

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1. ✅ What is Snapshot Testing?

Snapshot testing captures a visual representation (image or text) of your UI and compares it to a stored reference.

• The test fails when the current snapshot differs from the saved one.
• Commonly used for:
  • Visual regression detection
  • Layout validation with Dynamic Type
  • Theme testing (dark/light mode)

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2. 🧰 Available Frameworks for Snapshot Testing

Framework	Features
SnapshotTesting (Point-Free)	Swift-native, supports SwiftUI, UIKit, UIViewController, CALayer, Accessibility, etc.
iOSSnapshotTestCase (Uber/Facebook)	UIKit-focused, great for Objective-C or legacy UIKit codebases.
swift-snapshot-testing	Community-maintained alternative.

✅ Recommended: SnapshotTesting (Point-Free) for modern SwiftUI or Swift apps.

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3. 🧪 SwiftUI Example - CustomTextField

CustomTextField View

struct CustomTextField: View {
    let header: String
    let error: String?
    @Binding var text: String

    var body: some View {
        VStack(alignment: .leading, spacing: 12) {
            Text(header)
                .font(.title)
                .bold()
            if let error {
                Text(error)
                    .foregroundColor(.red)
                    .font(.subheadline)
            }
            TextField("Enter text...", text: $text)
                .textFieldStyle(.roundedBorder)
        }
        .accessibilityIdentifier("CustomTextFieldView_VoiceOver")
        .padding()
    }
}

ContentView View

struct ContentView: View {
    private var errorMessage: String? {
        isShowError ? "This is Demo error" : nil
    }

    @State private var inputText: String
    private let isShowError: Bool
    private let header: String

    init(header: String = "Header 1",
         inputText: String = "Sample demo",
         isShowError: Bool = false) {
        self.header = header
        self.inputText = inputText
        self.isShowError = isShowError
    }

    var body: some View {
        VStack(alignment: .leading, spacing: 0) {
            CustomTextField(
                header: header,
                error: errorMessage,
                text: $inputText
            )
            Spacer()
        }
    }
}

4. 🧪 Test Cases (XCTest + SnapshotTesting)

@MainActor
func test_customTextField_withoutError_snapshot() async throws {
    let view = ContentView()
    let vc = UIHostingController(rootView: view)
    assertSnapshot(matching: vc, as: .image(on: .iPhoneX), named: "CustomTextFieldView")
}

@MainActor
func test_customTextField_withError_snapshot() async throws {
    let view = ContentView(isShowError: true)
    let vc = UIHostingController(rootView: view)
    assertSnapshot(matching: vc, as: .image(on: .iPhoneX), named: "CustomTextFieldView_withError")
}

@MainActor
func test_customTextField_accessibilityLarge_snapshot() async throws {
    let traits = UITraitCollection(preferredContentSizeCategory: .accessibilityLarge)
    let vc = UIHostingController(rootView: ContentView())
    assertSnapshot(matching: vc, as: .image(on: .iPhoneX, traits: traits), named: "Accessibility_Large")
}

@MainActor
func test_contentView_accessibilityLabel_snapshot() async throws {
    let vc = UIHostingController(rootView: ContentView())
    assertSnapshot(matching: vc, as: .accessibilityDescription, named: "ContentView_accessibilityLabel")
}

5. ✅ Advantages vs 🚫 Disadvantages

✅ Advantages:

• Quickly detects UI regressions visually.
• Great for design consistency across font sizes/devices.
• Simplifies testing layout without verbose assertions.
• Easy integration with SwiftUI previews and components.

🚫 Disadvantages:

• Fragile: Fails on minor pixel variations.
• Harder to debug: No descriptive output—requires visual diff review.
• Needs frequent updates when intentional changes happen.
• Can create a lot of snapshot artifacts in the repo.

6. Best Practices

• Use .accessibilityDescription for accessibility snapshots.
• Name snapshots meaningfully with named: to avoid confusion.
• Always turn off isRecording = true before committing.
• Run tests consistently on the same device (e.g., .iPhoneX).
• Combine with unit tests for full coverage.