Add unit tests for ButtonBaseDesigner (#11690)

* Add unit tests for ButtonBaseDesigner

Author: LeafShi1

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

@@ -0,0 +1,56 @@
+// 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.Collections;
+
+namespace System.Windows.Forms.Design.Tests;
+
+public sealed class ButtonBaseDesignerTests
+{
+    [Fact]
+    public void ButtonBaseDesigner_Constructor_Initialize_AutoResizeHandles()
+    {
+        using ButtonBaseDesigner buttonBaseDesigner = new();
+
+        buttonBaseDesigner.AutoResizeHandles.Should().Be(true);
+    }
+
+    public static TheoryData<IDictionary<string, object>?> IDictionary_TheoryData => new()
+    {
+        null,
+        new Dictionary<string, object>()
+    };
+
+    [Theory]
+    [MemberData(nameof(IDictionary_TheoryData))]
+    public void ButtonBaseDesigner_InitializeNewComponent_WithDefaultButton(IDictionary<string, object>? defaultValues)
+    {
+        using ButtonBaseDesigner buttonBaseDesigner = new();
+        using Button button = new();
+        buttonBaseDesigner.Initialize(button);
+
+        buttonBaseDesigner.InitializeNewComponent((IDictionary?)defaultValues);
+        Assert.False(button.IsHandleCreated);
+    }
+
+    [Theory]
+    [MemberData(nameof(IDictionary_TheoryData))]
+    public void ButtonBaseDesigner_InitializeNewComponent_NotInitialized(IDictionary<string, object>? defaultValues)
+    {
+        using ButtonBaseDesigner buttonBaseDesigner = new();
+        Action action = () => buttonBaseDesigner.InitializeNewComponent((IDictionary?)defaultValues);
+        action.Should().Throw<InvalidOperationException>();
+    }
+
+    [Fact]
+    public void ButtonBaseDesigner_SnapLinesWithDefaultButton_ShouldReturnExpectedCount()
+    {
+        using ButtonBaseDesigner buttonBaseDesigner = new();
+        using Button button = new();
+        buttonBaseDesigner.Initialize(button);
+
+        buttonBaseDesigner.SnapLines.Count.Should().Be(9);
+    }
+}