Added new tests for all IMemoryGroup<T> enumerators

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

@@ -1,8 +1,10 @@
-// Copyright (c) Six Labors and contributors.
+// Copyright (c) Six Labors and contributors.
 // Licensed under the Apache License, Version 2.0.
 
 using System;
 using System.Buffers;
+using System.Collections;
+using System.Collections.Generic;
 using System.Linq;
 using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Memory;
@@ -165,7 +167,7 @@ namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
         }
 
         [Fact]
-        public void Fill()
+        public void FillWithFastEnumerator()
         {
             using MemoryGroup<int> group = this.CreateTestGroup(100, 10, true);
             group.Fill(42);
@@ -177,6 +179,34 @@ namespace SixLabors.ImageSharp.Tests.Memory.DiscontiguousBuffers
             }
         }
 
+        [Fact]
+        public void FillWithSlowGenericEnumerator()
+        {
+            using MemoryGroup<int> group = this.CreateTestGroup(100, 10, true);
+            group.Fill(42);
+
+            int[] expectedRow = Enumerable.Repeat(42, 10).ToArray();
+            IReadOnlyList<Memory<int>> groupAsList = group;
+            foreach (Memory<int> memory in groupAsList)
+            {
+                Assert.True(memory.Span.SequenceEqual(expectedRow));
+            }
+        }
+
+        [Fact]
+        public void FillWithSlowEnumerator()
+        {
+            using MemoryGroup<int> group = this.CreateTestGroup(100, 10, true);
+            group.Fill(42);
+
+            int[] expectedRow = Enumerable.Repeat(42, 10).ToArray();
+            IEnumerable groupAsList = group;
+            foreach (Memory<int> memory in groupAsList)
+            {
+                Assert.True(memory.Span.SequenceEqual(expectedRow));
+            }
+        }
+
         [Fact]
         public void Clear()
         {