Avoid encoding the same image twice

tests/ImageSharp.Tests/Formats/WebP/Vp8ResidualTests.cs

@@ -5,7 +5,7 @@ using SixLabors.ImageSharp.Formats.Webp.Lossy;
 using SixLabors.ImageSharp.Tests.TestUtilities;
 using Xunit;
 
-namespace SixLabors.ImageSharp.Tests.Formats.WebP
+namespace SixLabors.ImageSharp.Tests.Formats.Webp
 {
     [Trait("Format", "Webp")]
     public class Vp8ResidualTests

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

@@ -269,9 +269,9 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
         }
 
         [Theory]
-        [WithFile(TestImages.Png.Transparency, PixelTypes.Rgba32, false)]
-        [WithFile(TestImages.Png.Transparency, PixelTypes.Rgba32, true)]
-        public void Encode_Lossy_WithAlpha_Works<TPixel>(TestImageProvider<TPixel> provider, bool compressed)
+        [WithFile(TestImages.Png.Transparency, PixelTypes.Rgba32, false, 64020)]
+        [WithFile(TestImages.Png.Transparency, PixelTypes.Rgba32, true, 16200)]
+        public void Encode_Lossy_WithAlpha_Works<TPixel>(TestImageProvider<TPixel> provider, bool compressed, int expectedFileSize)
             where TPixel : unmanaged, IPixel<TPixel>
         {
             var encoder = new WebpEncoder()
@@ -281,33 +281,16 @@ namespace SixLabors.ImageSharp.Tests.Formats.Webp
             };
 
             using Image<TPixel> image = provider.GetImage();
-            image.VerifyEncoder(
+            string encodedFile = image.VerifyEncoder(
                 provider,
                 "webp",
                 $"with_alpha_compressed_{compressed}",
                 encoder,
                 ImageComparer.Tolerant(0.04f),
                 referenceDecoder: new MagickReferenceDecoder());
-        }
-
-        [Theory]
-        [WithFile(TestImages.Png.Transparency, PixelTypes.Rgba32)]
-        public void Encode_Lossy_WithCompressedAlpha_AlphaShouldBeSmaller<TPixel>(TestImageProvider<TPixel> provider)
-            where TPixel : unmanaged, IPixel<TPixel>
-        {
-            var encoder = new WebpEncoder()
-            {
-                FileFormat = WebpFileFormatType.Lossy,
-                UseAlphaCompression = true
-            };
 
-            using Image<TPixel> image = provider.GetImage();
-            using (var memoryStream = new MemoryStream())
-            {
-                image.SaveAsWebp(memoryStream, encoder);
-                int size = memoryStream.ToArray().Length;
-                Assert.True(size < 16300);
-            }
+            int encodedBytes = File.ReadAllBytes(encodedFile).Length;
+            Assert.True(encodedBytes <= expectedFileSize);
         }
 
         [Theory]

tests/ImageSharp.Tests/TestUtilities/TestImageExtensions.cs

@@ -661,7 +661,8 @@ namespace SixLabors.ImageSharp.Tests
         /// Loads the expected image with a reference decoder + compares it to <paramref name="image"/>.
         /// Also performs a debug save using <see cref="ImagingTestCaseUtility.SaveTestOutputFile{TPixel}"/>.
         /// </summary>
-        internal static void VerifyEncoder<TPixel>(
+        /// <returns>The path to the encoded output file.</returns>
+        internal static string VerifyEncoder<TPixel>(
             this Image<TPixel> image,
             ITestImageProvider provider,
             string extension,
@@ -687,6 +688,8 @@ namespace SixLabors.ImageSharp.Tests
                 ImageComparer comparer = customComparer ?? ImageComparer.Exact;
                 comparer.VerifySimilarity(encodedImage, image);
             }
+
+            return actualOutputFile;
         }
 
         internal static AllocatorBufferCapacityConfigurator LimitAllocatorBufferCapacity<TPixel>(