Fix broken test

tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs

@@ -19,6 +19,39 @@ namespace SixLabors.ImageSharp.Tests
     {
         private const PixelTypes PixelTypes = Tests.PixelTypes.Rgba32 | Tests.PixelTypes.RgbaVector | Tests.PixelTypes.Argb32;
 
+        // Contains the png marker, IHDR and pHYs chunks of a 1x1 pixel 32bit png 1 a single black pixel.
+        private static byte[] raw1x1PngIHDRAndpHYs =
+         {
+            // PNG Identifier 
+            0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A,
+            
+            // IHDR
+            0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x01, 0x08, 0x02, 0x00, 0x00, 0x00, 
+            // IHDR CRC
+            0x90, 0x77, 0x53, 0xDE, 
+
+            // pHYS
+            0x00, 0x00, 0x00, 0x09, 0x70, 0x48, 0x59, 0x73, 0x00, 0x00, 0x0E, 0xC3, 0x00, 0x00, 0x0E, 0xC3, 0x01, 
+            // pHYS CRC
+            0xC7, 0x6F, 0xA8, 0x64
+        };
+
+        // Contains the png marker, IDAT and IEND chunks of a 1x1 pixel 32bit png 1 a single black pixel.
+        private static byte[] raw1x1PngIDATAndIEND =
+          {
+            // IDAT
+            0x00, 0x00, 0x00, 0x0C, 0x49, 0x44, 0x41, 0x54, 0x18, 0x57, 0x63, 0x60, 0x60, 0x60, 0x00, 0x00,
+            0x00, 0x04, 0x00, 0x01, 
+            // IDAT CRC
+            0x5C, 0xCD, 0xFF, 0x69, 
+
+            // IEND
+            0x00, 0x00, 0x00, 0x00, 0x49, 0x45,
+            0x4E, 0x44, 
+            // IEND CRC
+            0xAE, 0x42, 0x60, 0x82
+        };
+
         public static readonly string[] CommonTestImages =
             {
                 TestImages.Png.Splash, TestImages.Png.Indexed,
@@ -210,11 +243,9 @@ namespace SixLabors.ImageSharp.Tests
         {
             using (var memStream = new MemoryStream())
             {
-                memStream.Skip(8);
-
+                WriteHeaderChunk(memStream);
                 WriteChunk(memStream, chunkName);
-
-                CompressStream(memStream);
+                WriteDataChunk(memStream);
 
                 var decoder = new PngDecoder();
 
@@ -230,23 +261,27 @@ namespace SixLabors.ImageSharp.Tests
         [Theory]
         [InlineData(PngChunkTypes.Gamma)]
         [InlineData(PngChunkTypes.PaletteAlpha)]
-        [InlineData(PngChunkTypes.Physical)]
+        [InlineData(PngChunkTypes.Physical)] // It's ok to test physical as we don't throw for duplicate chunks.
         //[InlineData(PngChunkTypes.Text)] //TODO: Figure out how to test this
         public void Decode_IncorrectCRCForNonCriticalChunk_ExceptionIsThrown(string chunkName)
         {
             using (var memStream = new MemoryStream())
             {
-                memStream.Skip(8);
-
+                WriteHeaderChunk(memStream);
                 WriteChunk(memStream, chunkName);
-
-                CompressStream(memStream);
+                WriteDataChunk(memStream);
 
                 var decoder = new PngDecoder();
                 decoder.Decode<Rgb24>(null, memStream);
             }
         }
 
+        private static void WriteHeaderChunk(MemoryStream memStream)
+        {
+            // Writes a 1x1 32bit png header chunk containing a single black pixel
+            memStream.Write(raw1x1PngIHDRAndpHYs, 0, raw1x1PngIHDRAndpHYs.Length);
+        }
+
         private static void WriteChunk(MemoryStream memStream, string chunkName)
         {
             memStream.Write(new byte[] { 0, 0, 0, 1 }, 0, 4);
@@ -254,13 +289,11 @@ namespace SixLabors.ImageSharp.Tests
             memStream.Write(new byte[] { 0, 0, 0, 0, 0 }, 0, 5);
         }
 
-        private static void CompressStream(Stream stream)
+        private static void WriteDataChunk(MemoryStream memStream)
         {
-            stream.Position = 0;
-            using (var deflateStream = new DeflateStream(stream, CompressionLevel.NoCompression, true))
-            {
-            }
-            stream.Position = 0;
+            // Writes a 1x1 32bit png data chunk containing a single black pixel
+            memStream.Write(raw1x1PngIDATAndIEND, 0, raw1x1PngIDATAndIEND.Length);
+            memStream.Position = 0;
         }
     }
 }