Fix broken chunk test

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

@@ -77,8 +77,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
         [Theory]
         [InlineData((uint)PngChunkType.Gamma)] // gAMA
         [InlineData((uint)PngChunkType.PaletteAlpha)] // tRNS
-        [InlineData(
-            (uint)PngChunkType.Physical)] // pHYs: It's ok to test physical as we don't throw for duplicate chunks.
+        [InlineData((uint)PngChunkType.Physical)] // pHYs: 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(uint chunkType)
         {
@@ -112,9 +111,11 @@ namespace SixLabors.ImageSharp.Tests.Formats.Png
 
         private static void WriteChunk(MemoryStream memStream, string chunkName)
         {
-            memStream.Write(new byte[] { 0, 0, 0, 1 }, 0, 4);
-            memStream.Write(Encoding.GetEncoding("ASCII").GetBytes(chunkName), 0, 4);
-            memStream.Write(new byte[] { 0, 0, 0, 0, 0 }, 0, 5);
+            // Needs a minimum length of 9 for pHYs chunk.
+            memStream.Write(new byte[] { 0, 0, 0, 9 }, 0, 4);
+            memStream.Write(Encoding.GetEncoding("ASCII").GetBytes(chunkName), 0, 4); // 4 bytes chunk header
+            memStream.Write(new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 0 }, 0, 9); // 9 bytes of chunk data
+            memStream.Write(new byte[] { 0, 0, 0, 0 }, 0, 4); // Junk Crc
         }
 
         private static void WriteDataChunk(MemoryStream memStream)