address some unrelated coverage issues reported by CodeCov for some reason

tests/ImageSharp.Tests/Image/ImageTests.cs

@@ -5,7 +5,9 @@ using System;
 using System.IO;
 using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Advanced;
+using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Jpeg;
+using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
@@ -324,5 +326,25 @@ namespace SixLabors.ImageSharp.Tests
                 Assert.Throws<ObjectDisposedException>(() => { var res = genericImage.CloneAs<Rgba32>(this.configuration); });
             }
         }
+
+        public class DetectEncoder
+        {
+            [Fact]
+            public void KnownExtension_ReturnsEncoder()
+            {
+                using var image = new Image<L8>(1, 1);
+                IImageEncoder encoder = image.DetectEncoder("dummy.png");
+                Assert.NotNull(encoder);
+                Assert.IsType<PngEncoder>(encoder);
+            }
+
+            [Fact]
+            public void UnknownExtension_ReturnsNull()
+            {
+                using var image = new Image<L8>(1, 1);
+                IImageEncoder encoder = image.DetectEncoder("dummy.yolo");
+                Assert.Null(encoder);
+            }
+        }
     }
 }

tests/ImageSharp.Tests/Memory/DiscontiguousBuffers/MemoryGroupTests.cs

@@ -119,6 +119,14 @@ namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
             Assert.True(group[0].Span.SequenceEqual(data0));
             Assert.True(group[1].Span.SequenceEqual(data1));
             Assert.True(group[2].Span.SequenceEqual(data2));
+
+            int cnt = 0;
+            int[][] allData = { data0, data1, data2 };
+            foreach (Memory<int> memory in group)
+            {
+                Assert.True(memory.Span.SequenceEqual(allData[cnt]));
+                cnt++;
+            }
         }
 
         public static TheoryData<long, int, long, int> GetBoundedSlice_SuccessData = new TheoryData<long, int, long, int>()