Snapshot-Driven UI Iteration

Use swift-snapshot-testing to create a visual feedback loop when implementing UI changes. Render SwiftUI views to PNG after each code change, compare against design goals, fix mismatches, and repeat.

When to Use

• Implementing UI from Figma designs or reference screenshots
• Multi-step view redesigns where each step should match a target
• Any SwiftUI work where you need to visually verify output
• When design reference images are available for comparison

When NOT to Use

• Simple single-property changes (color, font)
• Logic-only changes with no visual impact
• When the project already has snapshot tests covering the view

Core Flow

1. SETUP      Add swift-snapshot-testing dependency (temporary)
2. GOAL       Collect design reference images
3. SCAFFOLD   Create snapshot test rendering the target view
4. LOOP       For each implementation step:
                a. Edit code
                b. Run snapshot test (record mode)
                c. Read generated PNG
                d. Compare against design
                e. If mismatch -> fix and re-snapshot
                f. If match -> commit the verified change, move to next step
5. CLEANUP    Revert dependency + delete test file

Setup: Add Dependency

Check if swift-snapshot-testing already exists in Modules/Package.swift. If not, add it temporarily.

In the dependencies array of Modules/Package.swift:

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

In the relevant test target's dependencies array:

.product(name: "SnapshotTesting", package: "swift-snapshot-testing"),

Common test targets in this project:

• PointOfSaleTests — for POS views
• WooFoundationTests — for shared UI components
• YosemiteTests — for business logic views

Remember the original state of Modules/Package.swift so you can revert exactly after cleanup.

Goal: Collect References

If the user provides design reference images (Figma exports, screenshots):

mkdir -p ~/Downloads/snapshot_experiment
cp ~/path/to/design.png ~/Downloads/snapshot_experiment/design.png

Read each reference image to understand the target state before writing code.

If no reference image, the goal is inferred from the user's description of desired UI behavior.

Scaffold: Create Snapshot Test

Create a test file in the appropriate Modules/Tests/*Tests/ directory:

import XCTest
import SnapshotTesting
import SwiftUI
@testable import TargetModule

final class ViewNameSnapshotTests: XCTestCase {
    override func invokeTest() {
        withSnapshotTesting(record: .all) {
            super.invokeTest()
        }
    }

    func test_defaultState_snapshot() {
        let view = YourView(/* props for default state */)
            .frame(width: 375, height: 900)
        assertSnapshot(of: view, as: .image(layout: .sizeThatFits))
    }

    func test_alternateState_snapshot() {
        let view = YourView(/* props for alternate state */)
            .frame(width: 375, height: 900)
        assertSnapshot(of: view, as: .image(layout: .sizeThatFits))
    }
}

Important details for this project:

• record: .all in invokeTest() forces PNG generation every run
• For POS views, set .environment(\.horizontalSizeClass, .regular) — POS is iPad-first
• Use .frame(width:height:) to control render size. Start with height: 900, increase to 1200+ if content is clipped
• Tests will always "fail" in record mode — this is expected, they report recording, not comparison
• Use POS design tokens (POSPadding, POSSpacing, POSFontStyle, Color+POSColorPalette) when comparing POS designs

Run: Execute Snapshot Tests

Use the /simulator skill approach to discover a booted simulator UDID.

Run only the snapshot tests for fast feedback:

xcodebuild test \
  -workspace WooCommerce.xcworkspace \
  -scheme WooCommerce \
  -destination 'platform=iOS Simulator,id=<SIMULATOR_UDID>' \
  -only-testing:<TestTarget>/<SnapshotTestClass> \
  CODE_SIGNING_ALLOWED=NO 2>&1 | tail -30

Prefer module-level test targets over the full app for faster feedback (~25s vs minutes).

Generated PNGs appear at:

Modules/Tests/<TestTarget>/__Snapshots__/<TestClass>/test_name.1.png

Compare: Read and Assess

After each run:

1. Read the generated PNG using the Read tool
2. If a design reference exists, read it side by side
3. Identify specific mismatches: layout, spacing, missing elements, text wrapping, colors
4. Copy PNGs to working directory with step labels for history:

cp Modules/Tests/<Target>/__Snapshots__/<Class>/test_name.1.png ~/Downloads/snapshot_experiment/step1.png

Fix: Iterate on Mismatches

Common issues caught by snapshots:

• Text wrapping in pills/badges at narrow widths — add .lineLimit(1).fixedSize(horizontal: true, vertical: false), reduce padding
• Back button showing in non-compact context — set .environment(\.horizontalSizeClass, .regular)
• Content clipped at bottom — increase frame height in test
• Spacing mismatches — check POSPadding/POSSpacing values against design
• Wrong section order — compare VStack children order with design

When fixing: edit the code and re-run snapshots to verify. Only commit once the snapshot matches the design goal — don't commit untested changes.

Cleanup: Remove ALL Temporary Artifacts

After implementation is complete, revert ALL temporary changes:

# Revert Package.swift (removes snapshot dependency)
git checkout -- Modules/Package.swift

# Revert Package.resolved if it changed
git checkout -- Modules/Package.resolved

# Also revert workspace Package.resolved if changed
git checkout -- WooCommerce.xcworkspace/xcshareddata/swiftpm/Package.resolved

# Delete the snapshot test file
rm Modules/Tests/<TestTarget>/<SnapshotTestClass>.swift

# Delete generated snapshot directory
rm -rf Modules/Tests/<TestTarget>/__Snapshots__

# Verify clean state
git status

Critical: Never commit snapshot test files, __Snapshots__/ directories, or the swift-snapshot-testing dependency. These are temporary iteration tools only.

Quick Reference

Action	Command/Tool
Add dependency	Edit Modules/Package.swift
Run snapshots	xcodebuild test -only-testing:<Target>/<Class>
Find PNGs	Modules/Tests/<Target>/__Snapshots__/<Class>/test_name.1.png
View snapshot	Read tool on the PNG path
Compare	Read both snapshot PNG and design reference
Fix + re-run	Edit code, re-run xcodebuild, commit once verified
Clean up	git checkout -- Modules/Package.swift, rm test file + snapshots