Add code coverage for DataGridViewCellStyleConverter (#12462)

* Add code coverage for  DataGridViewCellStyleConverter

* Handle FeedBacks

* Handle FeedBacks

src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/DataGridViewCellStyleConverterTests.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.
+
+#nullable enable
+
+using System.ComponentModel.Design.Serialization;
+using System.Globalization;
+
+namespace System.Windows.Forms.Tests;
+
+public class DataGridViewCellStyleConverterTests
+{
+    private readonly DataGridViewCellStyleConverter _converter;
+    private readonly DataGridViewCellStyle _style;
+
+    public DataGridViewCellStyleConverterTests()
+    {
+        _converter = new();
+        _style = new();
+    }
+
+    [WinFormsFact]
+    public void CanConvertTo_InstanceDescriptor_ReturnsTrue()
+    {
+        _converter.CanConvertTo(null, typeof(InstanceDescriptor)).Should().BeTrue();
+    }
+
+    [WinFormsFact]
+    public void CanConvertTo_OtherType_ReturnsFalse()
+    {
+        _converter.CanConvertTo(null, typeof(int)).Should().BeFalse();
+    }
+
+    [WinFormsFact]
+    public void ConvertTo_InstanceDescriptor_ReturnsInstanceDescriptor()
+    {
+        object? convertTo = _converter.ConvertTo(null, CultureInfo.InvariantCulture, _style, typeof(InstanceDescriptor));
+        convertTo.Should().NotBeNull();
+        convertTo.Should().BeOfType<InstanceDescriptor>();
+    }
+
+    [WinFormsFact]
+    public void ConvertTo_UnsupportedType_ThrowsNotSupportedException()
+    {
+        Action action = () => _converter.ConvertTo(null, CultureInfo.InvariantCulture, _style, typeof(int));
+        action.Should().Throw<NotSupportedException>();
+    }
+}