Add code coverage for ListView.IconComparer (#13485)

* Add code coverage for ListView.IconComparer

* Update parameter name

---------

Co-authored-by: Leaf Shi <[email protected]>

Author: MelonWang1

src/test/unit/System.Windows.Forms/System/Windows/Forms/ListView.IconComparerTests.cs

@@ -0,0 +1,60 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Windows.Forms.Tests;
+
+public class ListView_IconComparerTests
+{
+    [WinFormsTheory]
+    [InlineData(SortOrder.Ascending)]
+    [InlineData(SortOrder.Descending)]
+    [InlineData(SortOrder.None)]
+    public void Constructor_SetsSortOrder_Correctly(SortOrder order)
+    {
+        ListView.IconComparer comparer = new(order);
+
+        ((SortOrder)comparer.TestAccessor().Dynamic._sortOrder).Should().Be(order);
+    }
+
+    [WinFormsTheory]
+    [InlineData(SortOrder.Ascending, SortOrder.Descending)]
+    [InlineData(SortOrder.Descending, SortOrder.Ascending)]
+    [InlineData(SortOrder.None, SortOrder.Ascending)]
+    public void SortOrder_Setter_UpdatesSortOrder(SortOrder initialOrder, SortOrder updatedOrder)
+    {
+        ListView.IconComparer comparer = new(initialOrder)
+        {
+            SortOrder = updatedOrder
+        };
+
+        ((SortOrder)comparer.TestAccessor().Dynamic._sortOrder).Should().Be(updatedOrder);
+    }
+
+    [WinFormsTheory]
+    [InlineData(SortOrder.Ascending, "A", "B", -1)]
+    [InlineData(SortOrder.Ascending, "B", "A", 1)]
+    [InlineData(SortOrder.Ascending, "A", "A", 0)]
+    [InlineData(SortOrder.Descending, "A", "B", 1)]
+    [InlineData(SortOrder.Descending, "B", "A", -1)]
+    [InlineData(SortOrder.Descending, "A", "A", 0)]
+    public void Compare_ComparesListViewItems_ByText_AndSortOrder(SortOrder order, string text1, string text2, int expectedSign)
+    {
+        ListView.IconComparer comparer = new(order);
+        ListViewItem item1 = new(text1);
+        ListViewItem item2 = new(text2);
+        int result = comparer.Compare(item1, item2);
+
+        Math.Sign(result).Should().Be(expectedSign);
+    }
+
+    [WinFormsFact]
+    public void Compare_NullItems_ReturnsExpected()
+    {
+        ListView.IconComparer comparer = new(SortOrder.Ascending);
+        ListViewItem item = new("A");
+
+        comparer.Compare(null, null).Should().Be(0);
+        comparer.Compare(null, item).Should().BeLessThan(0);
+        comparer.Compare(item, null).Should().BeGreaterThan(0);
+    }
+}