Add unit tests for ItemTypeToolStripMenuItem

src/System.Windows.Forms.Design/src/System/Windows/Forms/Design/ItemTypeToolStripMenuItem.cs

@@ -50,13 +50,13 @@ public override string? Text
         }
     }
 
-    public ToolboxItem TbxItem { get; set; } = s_invalidToolboxItem;
+    public ToolboxItem ToolboxItem { get; set; } = s_invalidToolboxItem;
 
     protected override void Dispose(bool disposing)
     {
         if (disposing)
         {
-            TbxItem = null!;
+            ToolboxItem = null!;
         }
 
         base.Dispose(disposing);

src/System.Windows.Forms.Design/tests/UnitTests/System/Windows/Forms/Design/ItemTypeToolStripMenuItemTests.cs

@@ -0,0 +1,64 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#nullable enable
+
+using System.Drawing;
+using System.Drawing.Design;
+
+namespace System.Windows.Forms.Design.Tests;
+
+public class ItemTypeToolStripMenuItemTests : IDisposable
+{
+    private readonly ItemTypeToolStripMenuItem _item;
+
+    public ItemTypeToolStripMenuItemTests()
+    {
+        _item = new ItemTypeToolStripMenuItem(typeof(string));
+    }
+
+    [Fact]
+    public void Constructor_SetsItemType()
+    {
+        _item.ItemType.Should().Be(typeof(string));
+    }
+
+    [Fact]
+    public void ConvertTo_SetAndGet()
+    {
+        _item.ConvertTo = true;
+        _item.ConvertTo.Should().BeTrue();
+    }
+
+    [Fact]
+    public void Image_Get_ReturnsCorrectImage()
+    {
+        _item.Image.Should().BeOfType<Bitmap>().Which.Should().Be(ToolStripDesignerUtils.GetToolboxBitmap(typeof(string)));
+    }
+
+    [Fact]
+    public void Text_ReturnsCorrectDescription()
+    {
+        _item.Text.Should().BeOfType<string>().Which.Should().Be(ToolStripDesignerUtils.GetToolboxDescription(typeof(string)));
+    }
+
+    [Fact]
+    public void ToolboxItem_SetAndGet()
+    {
+        ToolboxItem toolboxItem = new(typeof(string));
+        _item.ToolboxItem = toolboxItem;
+        _item.ToolboxItem.Should().Be(toolboxItem);
+    }
+
+    [Fact]
+    public void Dispose_SetsToolboxItemToNull()
+    {
+        _item.Dispose();
+        _item.ToolboxItem.Should().BeNull();
+    }
+
+    public void Dispose()
+    {
+        _item.Dispose();
+    }
+}