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📸 SnapshotTesting

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Delightful Swift snapshot testing.

Usage

Once installed, no additional configuration is required. You can import the SnapshotTesting module and call the assertSnapshot function.

import SnapshotTesting
import XCTest

class MyViewControllerTests: XCTestCase {
  func testMyViewController() {
    let vc = MyViewController()

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

When an assertion first runs, a snapshot is automatically recorded to disk and the test will fail, printing out the file path of any newly-recorded reference.

❌ failed - No reference was found on disk. Automatically recorded snapshot: …

open "…/MyAppTests/__Snapshots__/MyViewControllerTests/testMyViewController.png"

Re-run "testMyViewController" to test against the newly-recorded snapshot.

Repeat test runs will load this reference and compare it with the runtime value. If they don't match, the test will fail and describe the difference. Failures can be inspected from Xcode's Report Navigator or by inspecting the file URLs of the failure.

You can record a new reference by customizing snapshots inline with the assertion, or using the withSnapshotTesting tool:

// Record just this one snapshot
assertSnapshot(of: vc, as: .image, record: .all)

// Record all snapshots in a scope:
withSnapshotTesting(record: .all) {
  assertSnapshot(of: vc1, as: .image)
  assertSnapshot(of: vc2, as: .image)
  assertSnapshot(of: vc3, as: .image)
}

// Record all snapshots in an XCTestCase subclass:
class FeatureTests: XCTestCase {
  override func invokeTest() {
    withSnapshotTesting(record: .all) {
      super.invokeTest()
    }
  }
}

Snapshot Anything

While most snapshot testing libraries in the Swift community are limited to UIImages of UIViews, SnapshotTesting can work with any format of any value on any Swift platform!

The assertSnapshot function accepts a value and any snapshot strategy that value supports. This means that a view or view controller can be tested against an image representation and against a textual representation of its properties and subview hierarchy.

assertSnapshot(of: vc, as: .image)
assertSnapshot(of: vc, as: .recursiveDescription)

View testing is highly configurable. You can override trait collections (for specific size classes and content size categories) and generate device-agnostic snapshots, all from a single simulator.

assertSnapshot(of: vc, as: .image(on: .iPhoneSe))
assertSnapshot(of: vc, as: .recursiveDescription(on: .iPhoneSe))

assertSnapshot(of: vc, as: .image(on: .iPhoneSe(.landscape)))
assertSnapshot(of: vc, as: .recursiveDescription(on: .iPhoneSe(.landscape)))

assertSnapshot(of: vc, as: .image(on: .iPhoneX))
assertSnapshot(of: vc, as: .recursiveDescription(on: .iPhoneX))

assertSnapshot(of: vc, as: .image(on: .iPadMini(.portrait)))
assertSnapshot(of: vc, as: .recursiveDescription(on: .iPadMini(.portrait)))

Warning Snapshots must be compared using the exact same simulator that originally took the reference to avoid discrepancies between images.

Better yet, SnapshotTesting isn't limited to views and view controllers! There are a number of available snapshot strategies to choose from.

For example, you can snapshot test URL requests (e.g., those that your API client prepares).

assertSnapshot(of: urlRequest, as: .raw)
// POST http://localhost:8080/account
// Cookie: pf_session={"userId":"1"}
//
// email=blob%40pointfree.co&name=Blob

And you can snapshot test Encodable values against their JSON and property list representations.

assertSnapshot(of: user, as: .json)
// {
//   "bio" : "Blobbed around the world.",
//   "id" : 1,
//   "name" : "Blobby"
// }

assertSnapshot(of: user, as: .plist)
// <?xml version="1.0" encoding="UTF-8"?>
// <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
//  "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
// <plist version="1.0">
// <dict>
//   <key>bio</key>
//   <string>Blobbed around the world.</string>
//   <key>id</key>
//   <integer>1</integer>
//   <key>name</key>
//   <string>Blobby</string>
// </dict>
// </plist>

In fact, any value can be snapshot-tested by default using its mirror!

assertSnapshot(of: user, as: .dump)
// â–ż User
//   - bio: "Blobbed around the world."
//   - id: 1
//   - name: "Blobby"

If your data can be represented as an image, text, or data, you can write a snapshot test for it!

Documentation

The latest documentation is available here.

Installation

Xcode

Warning By default, Xcode will try to add the SnapshotTesting package to your project's main application/framework target. Please ensure that SnapshotTesting is added to a test target instead, as documented in the last step, below.

  1. From the File menu, navigate through Swift Packages and select Add Package Dependency….
  2. Enter package repository URL: https://github.com/pointfreeco/swift-snapshot-testing.
  3. Confirm the version and let Xcode resolve the package.
  4. On the final dialog, update SnapshotTesting's Add to Target column to a test target that will contain snapshot tests (if you have more than one test target, you can later add SnapshotTesting to them by manually linking the library in its build phase).

Swift Package Manager

If you want to use SnapshotTesting in any other project that uses SwiftPM, add the package as a dependency in Package.swift:

dependencies: [
  .package(
    url: "https://github.com/pointfreeco/swift-snapshot-testing",
    from: "1.12.0"
  ),
]

Next, add SnapshotTesting as a dependency of your test target:

targets: [
  .target(name: "MyApp"),
  .testTarget(
    name: "MyAppTests",
    dependencies: [
      "MyApp",
      .product(name: "SnapshotTesting", package: "swift-snapshot-testing"),
    ]
  )
]

Features

Plug-ins

Have you written your own SnapshotTesting plug-in? Add it here and submit a pull request!

Related Tools

Learn More

SnapshotTesting was designed with witness-oriented programming.

This concept (and more) are explored thoroughly in a series of episodes on Point-Free, a video series exploring functional programming and Swift hosted by Brandon Williams and Stephen Celis.

Witness-oriented programming and the design of this library was explored in the following Point-Free episodes:

<a href="https://www.pointfree.co/episodes/ep41-a-tour-of-snapshot-testing"> <img alt="video poster image" src="https://d3rccdn33rt8ze.cloudfront.net/episodes/0041.jpeg" width="480"> </a>

License

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