Add decoder tests for 2 bit bitmap's

tests/ImageSharp.Tests/Formats/Bmp/BmpDecoderTests.cs

@@ -131,6 +131,21 @@ namespace SixLabors.ImageSharp.Tests.Formats.Bmp
             }
         }
 
+        [Theory]
+        [WithFile(Bit2, PixelTypes.Rgba32)]
+        [WithFile(Bit2Color, PixelTypes.Rgba32)]
+        public void BmpDecoder_CanDecode_2Bit<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            using (Image<TPixel> image = provider.GetImage(BmpDecoder))
+            {
+                image.DebugSave(provider);
+
+                // Reference decoder cant decode 2-bit, compare to reference output instead.
+                image.CompareToReferenceOutput(provider, extension: "png");
+            }
+        }
+
         [Theory]
         [WithFile(Bit4, PixelTypes.Rgba32)]
         public void BmpDecoder_CanDecode_4Bit<TPixel>(TestImageProvider<TPixel> provider)

tests/ImageSharp.Tests/Formats/Bmp/BmpEncoderTests.cs

@@ -22,6 +22,8 @@ namespace SixLabors.ImageSharp.Tests.Formats.Bmp
     {
         private static BmpDecoder BmpDecoder => new();
 
+        private static BmpEncoder BmpEncoder => new();
+
         public static readonly TheoryData<BmpBitsPerPixel> BitsPerPixel =
         new()
         {
@@ -53,14 +55,12 @@ namespace SixLabors.ImageSharp.Tests.Formats.Bmp
         [MemberData(nameof(RatioFiles))]
         public void Encode_PreserveRatio(string imagePath, int xResolution, int yResolution, PixelResolutionUnit resolutionUnit)
         {
-            var options = new BmpEncoder();
-
             var testFile = TestFile.Create(imagePath);
             using (Image<Rgba32> input = testFile.CreateRgba32Image())
             {
                 using (var memStream = new MemoryStream())
                 {
-                    input.Save(memStream, options);
+                    input.Save(memStream, BmpEncoder);
 
                     memStream.Position = 0;
                     using (var output = Image.Load<Rgba32>(memStream))
@@ -78,14 +78,12 @@ namespace SixLabors.ImageSharp.Tests.Formats.Bmp
         [MemberData(nameof(BmpBitsPerPixelFiles))]
         public void Encode_PreserveBitsPerPixel(string imagePath, BmpBitsPerPixel bmpBitsPerPixel)
         {
-            var options = new BmpEncoder();
-
             var testFile = TestFile.Create(imagePath);
             using (Image<Rgba32> input = testFile.CreateRgba32Image())
             {
                 using (var memStream = new MemoryStream())
                 {
-                    input.Save(memStream, options);
+                    input.Save(memStream, BmpEncoder);
 
                     memStream.Position = 0;
                     using (var output = Image.Load<Rgba32>(memStream))

tests/Images/External/ReferenceOutput/BmpDecoderTests/BmpDecoder_CanDecode_2Bit_Rgba32_pal2.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:2c3e8b87af737c40d7be02e55a2aec93bb0e7bd123cd1f3e3b74482a0c7d18bd
+size 2376

tests/Images/External/ReferenceOutput/BmpDecoderTests/BmpDecoder_CanDecode_2Bit_Rgba32_pal2Color.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:c3da68e15f4edf6ce5da76360f3704d52baff5292ee12efe5415540b5788dda5
+size 2578