Write unit test for DataGridViewAddColumnDialog (dotnet#12662)

Related dotnet#10773

Proposed changes
Add unit test DataGridViewAddColumnDialogTests.cs for public properties and method of the DataGridViewAddColumnDialog.
Enable nullability in DataGridViewAddColumnDialogTests.cs.

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

@@ -0,0 +1,139 @@
+// 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.ComponentModel;
+using System.ComponentModel.Design;
+using System.ComponentModel.Design.Serialization;
+using System.Drawing;
+using System.Reflection;
+using Moq;
+
+namespace System.Windows.Forms.Design.Tests;
+
+public sealed class DataGridViewAddColumnDialogTests : IDisposable
+{
+    private readonly DataGridView _dataGridView = new();
+    private readonly Container _container = new();
+
+    public void Dispose()
+    {
+        _dataGridView.Dispose();
+        _container.Dispose();
+    }
+
+    [Fact]
+    public void Constructor_ShouldInitializeFields()
+    {
+        DataGridViewColumnCollection columns = _dataGridView.Columns;
+
+        Mock<ISite> mockSite = new();
+        Mock<IUIService> mockUIService = new();
+        using Font expectedFont = new("Arial", 12);
+
+        mockUIService.Setup(ui => ui.Styles["DialogFont"]).Returns(expectedFont);
+        mockSite.Setup(site => site.GetService(typeof(IUIService))).Returns(mockUIService.Object);
+        _dataGridView.Site = mockSite.Object;
+
+        using DataGridViewAddColumnDialog dialog = new(columns, _dataGridView);
+
+        DataGridViewColumnCollection dataGridViewColumns = (DataGridViewColumnCollection)dialog.TestAccessor().Dynamic._dataGridViewColumns;
+        using DataGridView liveDataGridView = (DataGridView)dialog.TestAccessor().Dynamic._liveDataGridView;
+
+        dialog.Should().NotBeNull();
+        dataGridViewColumns.Should().BeSameAs(columns);
+        liveDataGridView.Should().BeSameAs(_dataGridView);
+        dialog.Font.Should().Be(expectedFont);
+    }
+
+    [WinFormsTheory]
+    [InlineData(typeof(NoDesignerAttributeClass), null, null)]
+    [InlineData(typeof(WithDesignerAttributeClass), typeof(MockComponentDesigner), true)]
+    [InlineData(typeof(WithDesignerAttributeClass), typeof(MockComponentDesigner), false)]
+    public void GetComponentDesignerForType_ShouldReturnExpectedResult(Type type, Type? expectedDesignerType, bool? useTypeResolutionService)
+    {
+        ITypeResolutionService? typeResolutionService = useTypeResolutionService.HasValue && useTypeResolutionService.Value ? new MockTypeResolutionService() : null;
+
+        using ComponentDesigner? result = DataGridViewAddColumnDialog.GetComponentDesignerForType(typeResolutionService, type);
+
+        if (expectedDesignerType is null)
+        {
+            result.Should().BeNull();
+        }
+        else
+        {
+            result.Should().NotBeNull();
+            result.Should().BeOfType(expectedDesignerType);
+        }
+    }
+
+    private class NoDesignerAttributeClass
+    {
+    }
+
+    [Designer(typeof(MockComponentDesigner))]
+    private class WithDesignerAttributeClass
+    {
+    }
+
+    private class MockComponentDesigner : ComponentDesigner
+    {
+    }
+
+    private class MockTypeResolutionService : ITypeResolutionService
+    {
+        public Assembly GetAssembly(AssemblyName name) => throw new NotImplementedException();
+        public Assembly GetAssembly(AssemblyName name, bool throwOnError) => throw new NotImplementedException();
+        public string GetPathOfAssembly(AssemblyName name) => throw new NotImplementedException();
+        public Type? GetType(string name) => Type.GetType(name);
+        public Type? GetType(string name, bool throwOnError) => Type.GetType(name, throwOnError);
+        public Type? GetType(string name, bool throwOnError, bool ignoreCase) => Type.GetType(name, throwOnError, ignoreCase);
+        public void ReferenceAssembly(AssemblyName name) => throw new NotImplementedException();
+    }
+
+    [WinFormsTheory]
+    [InlineData("ValidName", false, false, false, true, true)]
+    [InlineData("DuplicateColumnName", true, false, false, true, false)]
+    [InlineData("DuplicateComponentName", false, true, false, true, false)]
+    [InlineData("InvalidIdentifier", false, false, true, true, false)]
+    [InlineData("DuplicateLiveColumnName", false, true, false, false, false)]
+    public void ValidName_ShouldReturnExpectedResult(string name, bool columnContains, bool containerContains, bool invalidIdentifier, bool allowDuplicateNameInLiveColumnCollection, bool expectedResult)
+    {
+        DataGridViewColumnCollection columns = _dataGridView.Columns;
+        if (columnContains)
+        {
+            columns.Add(new DataGridViewTextBoxColumn { Name = name });
+        }
+
+        if (containerContains)
+        {
+            _container.Add(new Component(), name);
+        }
+
+        NameCreationService nameCreationService = new(invalidIdentifier);
+        DataGridViewColumnCollection liveColumns = new(new DataGridView());
+        if (!allowDuplicateNameInLiveColumnCollection)
+        {
+            liveColumns.Add(new DataGridViewTextBoxColumn { Name = name });
+        }
+
+        bool result = DataGridViewAddColumnDialog.ValidName(name, columns, _container, nameCreationService, liveColumns, allowDuplicateNameInLiveColumnCollection);
+
+        result.Should().Be(expectedResult);
+    }
+
+    private class NameCreationService : INameCreationService
+    {
+        private readonly bool _invalidIdentifier;
+
+        public NameCreationService(bool invalidIdentifier)
+        {
+            _invalidIdentifier = invalidIdentifier;
+        }
+
+        public string CreateName(IContainer? container, Type dataType) => throw new NotImplementedException();
+        public bool IsValidName(string name) => !_invalidIdentifier;
+        public void ValidateName(string name) => throw new NotImplementedException();
+    }
+}