PreviewSnapshots

To use PreviewSnapshots in your previews, import PreviewSnapshots and define a static computed snapshots property on your PreviewProvider implementation.

1. Define a PreviewSnapshots<State> property where State is the type of data used to configure your view.
2. Provide an array of configurations using .init(name:state:).
3. Provide a configure closure that takes the state and returns the configured view.
4. Return snapshots.previews from the standard previews computed property.

Xcode will then generate an individual SwiftUI Preview for every configuration provided.

import PreviewSnapshots
import SwiftUI

struct ContentView: View {
    var message: String
    var isEnabled: Bool

    var body: some View { ... }
}

// MARK: - Previews

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        snapshots.previews.previewLayout(.sizeThatFits)
    }

    static var snapshots: PreviewSnapshots<String> {
        PreviewSnapshots(
            configurations: [
                .init(name: "Short Message", state: "Test"),
                .init(name: "Medium Message", state: "Medium length message"),
                .init(name: "Long Message", state: "This is a much longer message than the other messages being tested"),
            ],
            configure: { state in
                ContentView(message: state, isEnabled: true).padding()
            }
        )
    }
}

To run snapshot tests against your preview configurations, import PreviewSnapshotsTesting and call .assertSnapshots() on your PreviewProvider's snapshots property within an XCTestCase.

PreviewSnapshotsTesting will automatically generate a separate snapshot for each configuration defined in your snapshots property and compare them against the reference images on disk. You can also define multiple snapshot collections on a single PreviewProvider (e.g., disabledSnapshots) to group different test scenarios.

import PreviewSnapshotsTesting
import XCTest

@testable import ContentModule

final class ContentViewSnapshotTests: XCTestCase {
    func test_snapshots() {
        // Asserts all configurations defined in the snapshots property
        ContentView_Previews.snapshots.assertSnapshots()
    }

    func test_disabled_snapshots() {
        // Asserts a different collection of snapshots defined on the same provider
        ContentView_Previews.disabledSnapshots.assertSnapshots()
    }
}