Add code coverage for DataGridViewColumnTypeEditor (#13084)

Related #10773

Proposed changes
Add unit test file: DataGridViewColumnTypeEditor.cs for public methods of the DataGridViewColumnTypeEditor.cs

Author: Zheng-Li01

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

@@ -0,0 +1,93 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections;
+using System.ComponentModel;
+using System.ComponentModel.Design;
+using System.Drawing.Design;
+using Moq;
+
+namespace System.Windows.Forms.Design.Tests;
+
+public class DataGridViewColumnTypeEditorTests
+{
+    private readonly DataGridViewColumnTypeEditor _editor;
+
+    public DataGridViewColumnTypeEditorTests()
+    {
+        _editor = new();
+    }
+
+    [Fact]
+    public void Constructor_ShouldInitializeCorrectly()
+    {
+        _editor.Should().NotBeNull();
+        _editor.IsDropDownResizable.Should().BeTrue();
+    }
+
+    [Fact]
+    public void IsDropDownResizable_ShouldReturnTrue() =>
+        _editor.IsDropDownResizable.Should().BeTrue();
+
+    [Fact]
+    public void GetEditStyle_ShouldReturnDropDown() =>
+        _editor.GetEditStyle(null).Should().Be(UITypeEditorEditStyle.DropDown);
+
+    [Fact]
+    public void EditValue_ShouldReturnOriginalValue_WhenNoServiceProvider() =>
+        _editor.EditValue(null, null!, typeof(DataGridViewTextBoxColumn)).Should().Be(typeof(DataGridViewTextBoxColumn));
+
+    [Fact]
+    public void EditValue_ShouldReturnOriginalValue_WhenNoEditorService()
+    {
+        Mock<IServiceProvider> serviceProviderMock = new();
+        serviceProviderMock.Setup(sp => sp.GetService(typeof(IWindowsFormsEditorService))).Returns(null!);
+
+        _editor.EditValue(null, serviceProviderMock.Object, typeof(DataGridViewTextBoxColumn)).Should().Be(typeof(DataGridViewTextBoxColumn));
+    }
+
+    [Fact]
+    public void EditValue_ShouldReturnOriginalValue_WhenNoContextInstance()
+    {
+        Mock<IServiceProvider> serviceProviderMock = new();
+        Mock<IWindowsFormsEditorService> editorServiceMock = new();
+        serviceProviderMock.Setup(sp => sp.GetService(typeof(IWindowsFormsEditorService))).Returns(editorServiceMock.Object);
+
+        _editor.EditValue(null, serviceProviderMock.Object, typeof(DataGridViewTextBoxColumn)).Should().Be(typeof(DataGridViewTextBoxColumn));
+    }
+
+    [Fact]
+    public void EditValue_ShouldReturnOriginalValue_WhenSelectedTypeIsNull()
+    {
+        Mock<IServiceProvider> mockProvider = new();
+        Mock<IWindowsFormsEditorService> mockEditorService = new();
+        Mock<ITypeDescriptorContext> mockContext = new();
+        Mock<IDesignerHost> mockDesignerHost = new();
+        Mock<ITypeDiscoveryService> mockDiscoveryService = new();
+
+        mockProvider.Setup(p => p.GetService(typeof(IWindowsFormsEditorService)))
+                    .Returns(mockEditorService.Object);
+        mockProvider.Setup(p => p.GetService(typeof(IDesignerHost)))
+                    .Returns(mockDesignerHost.Object);
+        mockDesignerHost.Setup(d => d.GetService(typeof(ITypeDiscoveryService)))
+                        .Returns(mockDiscoveryService.Object);
+
+        ArrayList mockTypeCollection = [typeof(DataGridViewTextBoxColumn), typeof(DataGridViewCheckBoxColumn)];
+        mockDiscoveryService.Setup(d => d.GetTypes(typeof(DataGridViewColumn), false))
+                            .Returns(mockTypeCollection);
+
+        DataGridViewTextBoxColumn column = new();
+        SubListBoxItem listBoxItem = new(column);
+        mockContext.Setup(c => c.Instance).Returns(listBoxItem);
+
+        object? result = _editor.EditValue(mockContext.Object, mockProvider.Object, null);
+
+        mockEditorService.Verify(s => s.DropDownControl(It.IsAny<Control>()), Times.Once);
+        result.Should().Be(null);
+    }
+
+    private class SubListBoxItem : DataGridViewColumnCollectionDialog.ListBoxItem
+    {
+        public SubListBoxItem(DataGridViewColumn column) : base(column, null!, null!) { }
+    }
+}