🗜 SnapshotTestingHEIC

An extension to SnapshotTesting which allows you to create HEIC images. The benefit of using HEIC instead of PNG is that it can store as much as image quality as PNG, but with a smaller file size.

File Size Comparison

Real-world comparison using a complex UI layout (500x600 profile screen with gradients, shadows, cards, and text):

Format	Size	Savings
PNG	443 KB	-
HEIC Lossless	165 KB	63% smaller
HEIC Medium	31 KB	93% smaller
HEIC Maximum (lossy)	8 KB	98% smaller

You can verify this by looking at SnapshotTestingHEICTests.

Usage

Once installed, no additional configuration is required. You can import the SnapshotTestingHEIC module, call SnapshotTesting following their usage guide and simply provide our imageHEIC strategy as below.

import XCTest
import SnapshotTesting
import SnapshotTestingHEIC

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

    // Default (lossless quality)
    assertSnapshot(of: vc, as: .imageHEIC)

    // With compression quality options
    assertSnapshot(of: vc, as: .imageHEIC(compressionQuality: .lossless))  // Best quality, ~63% smaller than PNG
    assertSnapshot(of: vc, as: .imageHEIC(compressionQuality: .medium))    // Good quality, ~93% smaller than PNG
    assertSnapshot(of: vc, as: .imageHEIC(compressionQuality: .maximum))   // Smallest size, ~98% smaller than PNG
  }
}

Compression Quality Options

Option	Description
.lossless	Best quality, no compression artifacts (default)
.low	Minimal compression
.medium	Balanced quality and size
.high	Higher compression
.maximum	Smallest file size, some quality loss
.custom(Double)	Custom quality value (0.0 - 1.0)

Opaque Mode Options

You can also control how alpha channel is handled:

// Auto-detect (default) - automatically detects if image has transparency
assertSnapshot(of: vc, as: .imageHEIC(compressionQuality: .lossless, opaqueMode: .auto))

// Force opaque - no alpha channel
assertSnapshot(of: vc, as: .imageHEIC(compressionQuality: .lossless, opaqueMode: .opaque))

// Force transparent - with alpha channel
assertSnapshot(of: vc, as: .imageHEIC(compressionQuality: .lossless, opaqueMode: .transparent))

Option	Description
.auto	Automatically detect based on image's alpha info (default)
.opaque	Force opaque encoding (no alpha channel)
.transparent	Force transparent encoding (with alpha channel)

Known XCTest Warning

When running snapshot tests, you may see warnings like:

⭕️ ERROR: 'xctest' is trying to save an opaque image with 'AlphaLast'

This warning comes from XCTest internally, not from SnapshotTestingHEIC. It occurs when XCTest saves image attachments (reference, failure, difference) to the xcresult bundle. This is Apple's internal behavior and cannot be suppressed. The warning is informational only and does not affect the functionality or file sizes of your HEIC snapshots.

Installation

Xcode 11+

Warning: By default, Xcode will try to add the SnapshotTestingHEIC package to your project's main application/framework target. Please ensure that SnapshotTestingHEIC 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/alexey1312/SnapshotTestingHEIC
3. Confirm the version and let Xcode resolve the package
4. On the final dialog, update SnapshotTestingHEIC'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 SnapshotTestingHEIC to them by manually linking the library in its build phase)

Swift Package Manager

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

dependencies: [
  .package(url: "https://github.com/alexey1312/SnapshotTestingHEIC.git", from: "1.0.0"),
]

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

targets: [
  .target(
    name: "MyApp"
  ),

  .testTarget(
    name: "MyAppTests",
    dependencies: [
      .target(name: "MyApp"),
      .product(name: "SnapshotTestingHEIC", package: "SnapshotTestingHEIC"),
    ]
  ),
]

Other

We do not currently support distribution through CocoaPods or Carthage.

License

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