Change ConvertRgbToYuv with alpha test to use a fixed image as input

tests/ImageSharp.Tests/Formats/WebP/YuvConversionTests.cs

@@ -132,7 +132,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
         }
 
         [Theory]
-        [WithTestPatternImages(31, 31, PixelTypes.Rgba32)]
+        [WithFile(TestImages.Png.TestPattern31x31HalfTransparent, PixelTypes.Rgba32)]
         public void ConvertRgbToYuv_WithAlpha_Works<TPixel>(TestImageProvider<TPixel> provider)
             where TPixel : unmanaged, IPixel<TPixel>
         {
@@ -146,16 +146,6 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
             using System.Buffers.IMemoryOwner<byte> uBuffer = memoryAllocator.Allocate<byte>(uvWidth * image.Height);
             using System.Buffers.IMemoryOwner<byte> vBuffer = memoryAllocator.Allocate<byte>(uvWidth * image.Height);
 
-            // Make half of the the image transparent.
-            image.Mutate(c => c.ProcessPixelRowsAsVector4(row =>
-            {
-                int halfWidth = row.Length / 2;
-                for (int x = 0; x < halfWidth; x++)
-                {
-                    row[x] = new Vector4(row[x].X, row[x].Y, row[x].Z, 0.0f);
-                }
-            }));
-
             Span<byte> y = yBuffer.GetSpan();
             Span<byte> u = uBuffer.GetSpan();
             Span<byte> v = vBuffer.GetSpan();

tests/ImageSharp.Tests/TestImages.cs

@@ -59,6 +59,8 @@ namespace SixLabors.ImageSharp.Tests
             public const string PngWithMetadata = "Png/PngWithMetaData.png";
             public const string InvalidTextData = "Png/InvalidTextData.png";
             public const string David = "Png/david.png";
+            public const string TestPattern31x31 = "Png/testpattern31x31.png";
+            public const string TestPattern31x31HalfTransparent = "Png/testpattern31x31-halftransparent.png";
 
             // Filtered test images from http://www.schaik.com/pngsuite/pngsuite_fil_png.html
             public const string Filter0 = "Png/filter0.png";

tests/Images/Input/Png/testpattern31x31-halftransparent.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:415483fde21637bdf919244c0625665f4914f7678eb4e047507b9bcd2262ec50
+size 472

tests/Images/Input/Png/testpattern31x31.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:233dc410d723204dfd63c296ee3ca165f4a3641475627eb82f5515f31d25afe5
+size 484