readme.md

Meziantou.Framework.SnapshotTesting.SkiaSharp

Meziantou.Framework.SnapshotTesting.SkiaSharp extends Meziantou.Framework.SnapshotTesting with support for SkiaSharp images, enabling snapshot validation of SKImage, SKBitmap, SKPixmap, and SKSurface objects stored as PNG, JPEG, or WebP files.

Setup

Call AddSkiaSharp() on your SnapshotSettings to register the SkiaSharp serializer and comparer:

using System.Runtime.CompilerServices;
using Meziantou.Framework.SnapshotTesting;
using Meziantou.Framework.SnapshotTesting.SkiaSharp;

internal static class SnapshotConfiguration
{
    [ModuleInitializer]
    internal static void Initialize()
    {
        SnapshotSettings.Default.AddSkiaSharp();
    }
}

Then validate images from your tests:

public sealed class SampleTests
{
    [Fact]
    public void ValidateImage()
    {
        using var bitmap = SKBitmap.Decode("sample.png");
        Snapshot.Validate(bitmap, SnapshotType.Png);
    }
}

Important

Register once for the whole test assembly, not inside a test method. SnapshotSettings.Default is shared by every test in the process and its collections are not safe for concurrent modification, so calling AddSkiaSharp() from a test races against any other test that is serializing a snapshot at the same time. Repeated calls also append a serializer and a converter every time.

Note that SkiaSharp requires the native libraries to be available at runtime. They are included in the SkiaSharp package for Windows and macOS. On Linux, add a reference to SkiaSharp.NativeAssets.Linux.

Image comparison

By default, images are compared pixel-by-pixel (exact comparison). To allow minor rendering differences, configure a Structural Similarity Index (SSIM) threshold:

// In the module initializer shown above
SnapshotSettings.Default.AddSkiaSharp(new ImageComparisonSettings
{
    SimilarityThreshold = 0.99f, // 0.0 = completely different, 1.0 = identical
});

When SimilarityThreshold is set, the mean SSIM across the R, G, and B channels is computed and must be greater than or equal to the threshold for the images to be considered equal.