Add unit tests for ButtonBaseDesigner

Author: LeafShi1

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

@@ -0,0 +1,48 @@
+// 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;
+
+namespace System.Windows.Forms.Design.Tests;
+
+public class ButtonBaseDesignerTests
+{
+    [Fact]
+    public void ButtonBaseDesigner_Constructor_InitializesProperties()
+    {
+        using ButtonBaseDesigner buttonBaseDesigner = new();
+        using Button button = new();
+        buttonBaseDesigner.Initialize(button);
+        bool autoResizeHandles = buttonBaseDesigner.AutoResizeHandles;
+
+        buttonBaseDesigner.Should().NotBeNull();
+        autoResizeHandles.Should().Be(true);
+    }
+
+    public static IEnumerable<object[]> IDictionary_TestData()
+    {
+        yield return new object[] { null };
+        yield return new object[] { new Dictionary<string, object>() };
+    }
+
+    [Theory]
+    [MemberData(nameof(IDictionary_TestData))]
+    public void ButtonBaseDesigner_InitializeNewComponent_WithDefaultButton(IDictionary defaultValues)
+    {
+        using ButtonBaseDesigner buttonBaseDesigner = new();
+        using Button button = new();
+
+        buttonBaseDesigner.Initialize(button);
+        buttonBaseDesigner.InitializeNewComponent(defaultValues);
+    }
+
+    [Fact]
+    public void ButtonBaseDesigner_SnapLinesWithDefaultButton_ShouldReturnExpectedCount()
+    {
+        using ButtonBaseDesigner buttonBaseDesigner = new();
+        using Button button = new();
+        buttonBaseDesigner.Initialize(button);
+
+        buttonBaseDesigner.SnapLines.Count.Should().Be(9);
+    }
+}