Add unit tests for FocusableLabel

src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/FocusableLabelTests.cs

@@ -0,0 +1,58 @@
+// 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.Reflection;
+
+namespace System.Windows.Forms;
+
+public class FocusableLabelTests
+{
+    [Fact]
+    public void UnderlineWhenFocused_ShouldBeTrue()
+    {
+        using FocusableLabel label = new();
+
+        label.UnderlineWhenFocused.Should().BeTrue();
+    }
+
+    [Fact]
+    public void UnderlineWhenFocused_SetToFalse_ShouldBeFalse()
+    {
+        using FocusableLabel label = new();
+
+        label.UnderlineWhenFocused = false;
+
+        label.UnderlineWhenFocused.Should().BeFalse();
+    }
+
+    [Fact]
+    public void CreateParams_ClassName_ShouldBeNull()
+    {
+        using FocusableLabel label = new();
+
+        var createParams = GetCreateParams(label);
+
+        createParams.Should().NotBeNull();
+
+        var className = createParams?.GetType().GetProperty("ClassName")?.GetValue(createParams);
+
+        className.Should().BeNull();
+    }
+
+    private static object? GetCreateParams(Control control)
+    {
+        return typeof(Control)
+        .GetProperty("CreateParams", BindingFlags.NonPublic | BindingFlags.Instance)?
+        .GetValue(control);
+    }
+
+    [Fact]
+    public void TabStop_ShouldBeTrue()
+    {
+        using FocusableLabel label = new();
+
+        label.TabStop.Should().BeTrue("Expected TabStop to be true, indicating the control is selectable.");
+    }
+}