Snapshot Test Setup Skill for Claude

Without snapshots:        With snapshots:
Change a modifier         Change a modifier
  → Looks fine locally      → Snapshot test fails
  → Push to main            → Shows exact visual diff
  → User reports UI bug     → Fix before merging
  → Embarrassing             → Confidence in UI changes

Glob: **/Package.swift or **/*.xcodeproj
Grep: "swift-snapshot-testing" (already added?)
Grep: "SnapshotTesting" in test files

// Package.swift
dependencies: [
    .package(
        url: "https://github.com/pointfreeco/swift-snapshot-testing",
        from: "1.17.0"
    )
]

// Test target
.testTarget(
    name: "YourAppTests",
    dependencies: [
        "YourApp",
        .product(name: "SnapshotTesting", package: "swift-snapshot-testing")
    ]
)

import Testing
import SnapshotTesting
import SwiftUI
@testable import YourApp

// MARK: - Snapshot Configuration

enum SnapshotConfig {
    // iOS devices to test
    static let iPhoneConfigs: [String: ViewImageConfig] = [
        "iPhone_SE": .iPhoneSe,
        "iPhone_16": .iPhone13,       // Similar dimensions
        "iPhone_16_Pro_Max": .iPhone13ProMax
    ]

    // macOS window sizes
    static let macOSConfigs: [String: CGSize] = [
        "compact": CGSize(width: 400, height: 600),
        "regular": CGSize(width: 800, height: 600),
        "wide": CGSize(width: 1200, height: 800)
    ]

    // Color schemes to test
    static let colorSchemes: [ColorScheme] = [.light, .dark]
}

@Suite("Snapshots: HomeView")
struct HomeViewSnapshotTests {

    // perceptualPrecision < 1.0 absorbs GPU/anti-aliasing noise across runs
    // on the same pinned simulator — 0.98 catches real layout/color changes
    // while ignoring sub-perceptual rendering jitter.
    @Test("matches reference - light mode")
    func lightMode() {
        let view = HomeView(items: Item.sampleList)

        assertSnapshot(
            of: UIHostingController(rootView: view),
            as: .image(on: .iPhone13, perceptualPrecision: 0.98)
        )
    }

    @Test("matches reference - dark mode")
    func darkMode() {
        let view = HomeView(items: Item.sampleList)
            .environment(\.colorScheme, .dark)

        assertSnapshot(
            of: UIHostingController(rootView: view),
            as: .image(on: .iPhone13, perceptualPrecision: 0.98)
        )
    }

    @Test("matches reference - empty state")
    func emptyState() {
        let view = HomeView(items: [])

        assertSnapshot(
            of: UIHostingController(rootView: view),
            as: .image(on: .iPhone13, perceptualPrecision: 0.98)
        )
    }

    @Test("matches reference - accessibility Dynamic Type")
    func dynamicTypeAccessibility() {
        let view = HomeView(items: Item.sampleList)
            .environment(\.dynamicTypeSize, .accessibility3)

        assertSnapshot(
            of: UIHostingController(rootView: view),
            as: .image(on: .iPhone13, perceptualPrecision: 0.98)
        )
    }
}

@Suite("Snapshots: SettingsView")
struct SettingsViewSnapshotTests {

    @Test("matches reference - standard size")
    func standardSize() {
        let view = SettingsView()
            .frame(width: 500, height: 400)

        assertSnapshot(
            of: NSHostingController(rootView: view),
            as: .image(size: CGSize(width: 500, height: 400))
        )
    }

    @Test("matches reference - dark mode")
    func darkMode() {
        let view = SettingsView()
            .frame(width: 500, height: 400)
            .environment(\.colorScheme, .dark)

        assertSnapshot(
            of: NSHostingController(rootView: view),
            as: .image(size: CGSize(width: 500, height: 400))
        )
    }
}

@Suite("Snapshots: ItemCard")
struct ItemCardSnapshotTests {

    @Test("default state")
    func defaultState() {
        let view = ItemCard(item: .sample)
            .frame(width: 300)

        assertSnapshot(of: view, as: .image)
    }

    @Test("selected state")
    func selectedState() {
        let view = ItemCard(item: .sample, isSelected: true)
            .frame(width: 300)

        assertSnapshot(of: view, as: .image)
    }

    @Test("long title wraps")
    func longTitle() {
        let item = Item(title: "This is a very long title that should wrap to multiple lines")
        let view = ItemCard(item: item)
            .frame(width: 300)

        assertSnapshot(of: view, as: .image)
    }
}

# Record all snapshots (first run)
xcodebuild test -scheme YourApp \
  -destination 'platform=iOS Simulator,name=iPhone 16'

Tests/SnapshotTests/
├── __Snapshots__/
│   └── HomeViewSnapshotTests/
│       ├── lightMode.1.png
│       ├── darkMode.1.png
│       ├── emptyState.1.png
│       └── dynamicTypeXXL.1.png
├── HomeViewSnapshotTests.swift
└── ItemCardSnapshotTests.swift

// Temporarily set record mode
@Test("matches reference - light mode")
func lightMode() {
    withSnapshotTesting(record: .all) {
        let view = HomeView(items: Item.sampleList)
        assertSnapshot(
            of: UIHostingController(rootView: view),
            as: .image(on: .iPhone13)
        )
    }
}

- name: Run Snapshot Tests
  run: |
    xcodebuild test \
      -scheme YourApp \
      -destination 'platform=iOS Simulator,name=iPhone 16,OS=18.0' \
      -only-testing "YourAppTests/Snapshots" \
      -resultBundlePath TestResults.xcresult

- name: Upload Failed Snapshots
  if: failure()
  uses: actions/upload-artifact@v4
  with:
    name: failed-snapshots
    path: "**/Failures/**"

# ci_scripts/ci_post_xcodebuild.sh
if [ "$CI_XCODEBUILD_ACTION" = "test" ]; then
    # Upload snapshot failures as artifacts
    if [ -d "$CI_DERIVED_DATA_PATH" ]; then
        find "$CI_DERIVED_DATA_PATH" -name "Failures" -type d \
            -exec cp -r {} "$CI_RESULT_BUNDLE_PATH/" \;
    fi
fi

## Snapshot Tests Setup

### Dependency Added
swift-snapshot-testing 1.17.0 via SPM

### Tests Generated
| View | Configurations | Tests |
|------|---------------|-------|
| HomeView | light, dark, empty, XXL type | 4 |
| SettingsView | light, dark | 2 |
| ItemCard | default, selected, long title | 3 |
| **Total** | | **9** |

### Files Created
- `Tests/SnapshotTests/HomeViewSnapshotTests.swift`
- `Tests/SnapshotTests/SettingsViewSnapshotTests.swift`
- `Tests/SnapshotTests/ItemCardSnapshotTests.swift`

### Next Steps
1. Run tests once to record reference images
2. Commit `__Snapshots__/` directories to git
3. Add snapshot test step to CI pipeline