Delightful Swift snapshot testing.
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(matching: 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.
You can record a new reference by setting the record
mode to true
on the assertion or globally.
assertSnapshot(matching: vc, as: .image, record: true)
// or globally
record = true
assertSnapshot(matching: vc, as: .image)
While most snapshot testing libraries in the Swift community are limited to UIImage
s of UIView
s, 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(matching: vc, as: .image)
assertSnapshot(matching: 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(matching: vc, as: .image(on: .iPhoneSe))
assertSnapshot(matching: vc, as: .recursiveDescription(on: .iPhoneSe))
assertSnapshot(matching: vc, as: .image(on: .iPhoneSe(.landscape)))
assertSnapshot(matching: vc, as: .recursiveDescription(on: .iPhoneSe(.landscape)))
assertSnapshot(matching: vc, as: .image(on: .iPhoneX))
assertSnapshot(matching: vc, as: .recursiveDescription(on: .iPhoneX))
assertSnapshot(matching: vc, as: .image(on: .iPadMini(.portrait)))
assertSnapshot(matching: vc, as: .recursiveDescription(on: .iPadMini(.portrait)))
⚠️ Warning: Snapshots must be compared using a simulator with the same OS, device gamut, and scale as the 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(matching: 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(matching: user, as: .json)
// {
// "bio" : "Blobbed around the world.",
// "id" : 1,
// "name" : "Blobby"
// }
assertSnapshot(matching: 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(matching: user, as: .dump)
// ▿ 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! Check out all of the snapshot strategies that ship with SnapshotTesting and learn how to define your own custom strategies.
⚠️ Warning: By default, Xcode will try to add the SnapshotTesting package to your project's targets. Please uncheck SnapshotTesting in the final step of adding a Swift package to your target, as documented below.
- From the File menu, navigate through Swift Packages and select Add Package Dependency….
- Enter package respository URL:
https://github.com/pointfreeco/swift-snapshot-testing.git
- Confirm the version and let Xcode resolve the package
- On the final dialog, uncheck any box that adds the SnapshotTesting package to any target
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.git", from: "1.6.0"),
]
Next, add SnapshotTesting
as a dependency of your test target:
targets: [
.target(name: "MyApp", dependencies: [], path: "Sources"),
.testTarget(name: "MyAppTests", dependencies: ["MyApp", "SnapshotTesting"])
]
If you use Carthage, you can add the following dependency to your Cartfile
:
github "pointfreeco/swift-snapshot-testing" ~> 1.6
⚠️ Warning: Carthage instructs you to drag frameworks into your Xcode project. Xcode may automatically attempt to link these frameworks to your app target.SnapshotTesting.framework
is only compatible with test targets, so when you first add it to your project:
- Remove
SnapshotTesting.framework
from any non-test target it may have been added to.- Add
SnapshotTesting.framework
to any applicable test targets.- Add a New Copy Build Phase to any applicable test targets with Destination set to "Frameworks", and add
SnapshotTesting.framework
as an item to this phase.- Do not add
SnapshotTesting.framework
to the "Input Files" or "Output Files" of your app target's Carthagecopy-frameworks
Run Script Phase.See Carthage's "Adding frameworks to unit tests or a framework" documentation for more.
If your project uses CocoaPods, add the pod to any applicable test targets in your Podfile
:
target 'MyAppTests' do
pod 'SnapshotTesting', '~> 1.6'
end
- Dozens of snapshot strategies. Snapshot testing isn't just for
UIView
s andCALayer
s. Write snapshots against any value. - Write your own snapshot strategies. If you can convert it to an image, string, data, or your own diffable format, you can snapshot test it! Build your own snapshot strategies from scratch or transform existing ones.
- No configuration required. Don't fuss with scheme settings and environment variables. Snapshots are automatically saved alongside your tests.
- More hands-off. New snapshots are recorded whether
record
mode istrue
or not. - Subclass-free. Assert from any XCTest case or Quick spec.
- Device-agnostic snapshots. Render views and view controllers for specific devices and trait collections from a single simulator.
- First-class Xcode support. Image differences are captured as XCTest attachments. Text differences are rendered in inline error messages.
- Supports any platform that supports Swift. Write snapshot tests for iOS, Linux, macOS, and tvOS.
- SceneKit, SpriteKit, and WebKit support. Most snapshot testing libraries don't support these view subclasses.
Codable
support. Snapshot encodable data structures into their JSON and property list representations.- Custom diff tool integration.
-
swift-snapshot-testing-nimble adds Nimble matchers for SnapshotTesting.
-
swift-html is a Swift DSL for type-safe, extensible, and transformable HTML documents and includes an
HtmlSnapshotTesting
module to snapshot test its HTML documents.
Have you written your own SnapshotTesting plug-in? Add it here and submit a pull request!
-
iOSSnapshotTestCase
helped introduce screen shot testing to a broad audience in the iOS community. Experience with it inspired the creation of this library. -
Jest brought generalized snapshot testing to the JavaScript community with a polished user experience. Several features of this library (diffing, automatically capturing new snapshots) were directly influenced.
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:
- Episode 33: Protocol Witnesses: Part 1
- Episode 34: Protocol Witnesses: Part 2
- Episode 35: Advanced Protocol Witnesses: Part 1
- Episode 36: Advanced Protocol Witnesses: Part 2
- Episode 37: Protocol-Oriented Library Design: Part 1
- Episode 38: Protocol-Oriented Library Design: Part 2
- Episode 39: Witness-Oriented Library Design
- Episode 40: Async Functional Refactoring
- Episode 41: A Tour of Snapshot Testing 🆓
This library is released under the MIT license. See LICENSE for details.