PreviewSnapshots

Library for sharing view configurations between SwiftUI previews and SnapshotTesting snapshot tests.

Usage

In Previews

Import PreviewSnapshots and define a static computed snapshots property on the PreviewProvider implementation.

Provide as many configurations as you’d like within snapshots and then return snapshots.previews from the previews computed property.

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()
            }
        )
    }
}

Xcode will create an individual SwiftUI Preview for each configuration that’s provided.

In Snapshot Tests

Import PreviewSnapshotsTesting and call ContentView_Previews.snapshots.assertSnapshots() within a test.

PreviewSnapshotsTesting will generate a separate snapshot for each configuration defined within snapshots and compare the to the reference on disk.

See the SnapshotTesting library for additional information on snapshot testing.

import PreviewSnapshotsTesting
import XCTest

@testable import ContentModule

final class ContentViewSnapshotTests: XCTestCase {
    func test_snapshots() {
        ContentView_Previews.snapshots.assertSnapshots()
    }

    func test_disabled_snapshots() {
        // `PreviewProvider` can define multiple `PreviewSnapshot` collections to group like tests.
        ContentView_Previews.disabledSnapshots.assertSnapshots()
    }
}

Installation

Xcode

1. From the File menu select Add Packags….
2. Enter package repository URL: https://github.com/doordash-oss/swiftui-preview-snapshots
3. Confirm the version and let Xcode resolve the package
4. On the final dialog, ensure the Add to Target column for PreviewSnapshots is set to the app target and update the Add to Target column for PreviewSnapshotsTesting to the app’s test target

Swift Package Manager

1. Add the package as a dependency in Package.swift:

dependencies: [
    .package(url: "https://github.com/doordash-oss/swiftui-preview-snapshots", from: "1.0.0"),
]

2. Add PreviewSnapshots and PreviewSnapshotsTesting as a dependency of your primary and test targets respectively:

targets: [
    .target(
        name: "MyGreatApp"
        dependencies: [
            .product(name: "PreviewSnapshots", package: "swiftui-preview-snapshots"),
        ]
    ),
    .testTarget(
        name: "MyGreatAppTests",
        dependencies: [
            "MyGreatApp",
            .product(name: "PreviewSnapshotsTesting", package: "swiftui-preview-snapshots"),
        ]
    )
]

Acknowledgement

PreviewSnapshots drew inspiration from this talk by Nataliya Patsovska Marmelstein

License

This library is released under the Apache 2.0 license. See LICENSE for details.