Missing unit tests coverage of public methods in Design namespace

We are in the process of adding unit tests for all public methods to improve the test coverage of code. Here is a list categorized by namespace.

System.Windows.Forms.Design
- [x] AxImporter.cs https://github.com/dotnet/winforms/pull/11784
- [x] BaseContextMenuStrip.cs https://github.com/dotnet/winforms/pull/11723
- [x] BindingNavigatorDesigner.cs #13883
- [x] BindingSourceDesigner.cs https://github.com/dotnet/winforms/pull/11775
- [x] ButtonBaseDesigner.cs https://github.com/dotnet/winforms/pull/11690
- [x] ChangeToolStripParentVerb.cs #13445
- [x] CollectionEditVerbManager.cs #12088
- [x] ComboBoxDesigner.cs #10772
- [x] CommandSet.cs https://github.com/dotnet/winforms/pull/12769
- [x] ComponentDesigner #1053
- [x] ComponentTray.cs #13396
- [x] CompositionDesigner.cs https://github.com/dotnet/winforms/pull/11888
- [x] ContextMenuStripActionList.cs https://github.com/dotnet/winforms/pull/12442
- [x] ContextMenuStripGroup.cs https://github.com/dotnet/winforms/pull/11989
- [x] ContextMenuStripGroupCollection.cs https://github.com/dotnet/winforms/pull/11952
- [x] ControlCodeDomSerializer.cs #13011
- [x] ControlCommandSet.cs https://github.com/dotnet/winforms/pull/13130
- [x] ControlDesigner.ControlDesignerAccessibleObject.cs https://github.com/dotnet/winforms/pull/12664
- [x] ControlDesigner.DesignerControlCollection.cs https://github.com/dotnet/winforms/pull/12085
- [x] ControlDesigner.TransparentBehavior.cs https://github.com/dotnet/winforms/pull/12694
- [x] ControlDesigner.cs https://github.com/dotnet/winforms/pull/12410
- [x] CustomMenuItemCollection.cs #12035
- [x] DataGridViewAddColumnDialog.cs https://github.com/dotnet/winforms/pull/12662
- [x] DataGridViewCellStyleBuilder.cs https://github.com/dotnet/winforms/pull/12318
- [x] DataGridViewCellStyleEditor.cs #2684
- [x] DataGridViewColumnDesigner.cs https://github.com/dotnet/winforms/pull/12355
- [x] DataGridViewComponentPropertyGridSite.cs https://github.com/dotnet/winforms/pull/12357
- [x] DataGridViewColumnTypeEditor #13084
- [x] DataGridViewColumnType.Picker #13055
- [x] DataGridViewDesigner.cs #13014
- [x] DataSourceDescriptorCollection.cs https://github.com/dotnet/winforms/pull/12432
- [x] DataSourceGroupCollection.cs https://github.com/dotnet/winforms/pull/12430
- [x] DataSourceListEditor.cs #13122
- [x] DateTimePickerDesigner.cs https://github.com/dotnet/winforms/pull/11702
- [x] DesignBinding.cs https://github.com/dotnet/winforms/pull/11748
- [x] DesignBindingPicker.cs #13536
- [x] DesignBindingValueUIHandler #13100
- [x] DesignerExtenders.cs https://github.com/dotnet/winforms/pull/12337
- [x] DesignerFrame.cs https://github.com/dotnet/winforms/pull/12712
- [x] DesignerToolStripControlHost.cs https://github.com/dotnet/winforms/pull/12086
- [x] DesignerUtils.cs #13341 #13384 #13435
- [x] DesignerVerbToolStripMenuItem.cs https://github.com/dotnet/winforms/pull/12566
- [x] DocumentDesigner.cs
- [x] EditorServiceContext.cs #13273
- [x] FlowPanelDesigner.cs https://github.com/dotnet/winforms/pull/11735
- [x] FolderNameEditor.cs https://github.com/dotnet/winforms/pull/11973
- [ ] FormDocumentDesigner.cs
- [x] ~~FormatControl.CurrencyFormatType.cs~~ _(private class)_
- [x] ~~FormatControl.CustomFormatType.cs~~ _(private class)_
- [x] ~~FormatControl.DateTimeFormatType.cs~~ _(private class)_
- [x] ~~FormatControl.NoFormattingFormatType.cs~~ _(private class)_
- [x] ~~FormatControl.NumericFormatType.cs~~ _(private class)_
- [x] ~~FormatControl.ScientificFormatType.cs~~ _(private class)_
- [x] FormatControl.cs https://github.com/dotnet/winforms/pull/12168
- [x] FormatStringDialog.cs https://github.com/dotnet/winforms/pull/12185
- [x] FormatStringEditor.cs https://github.com/dotnet/winforms/pull/12208
- [x] FlowLayoutPanelDesigner #13257
- [x] GroupedContextMenuStrip.cs #11183
- [x] ImageCollectionCodeDomSerializer.cs #12753
- [x] ImageIndexEditor.cs https://github.com/dotnet/winforms/pull/12237
- [x] ImageListActionList.cs https://github.com/dotnet/winforms/pull/11766
- [x] ImageListDesigner.OriginalImageCollection.cs #12282
- [x] ImageListDesigner.cs https://github.com/dotnet/winforms/pull/11725
- [x] ImageListImage.cs https://github.com/dotnet/winforms/pull/11736
- [x] ImageListImageEditor.cs https://github.com/dotnet/winforms/pull/3404
- [x] InheritanceUI.cs https://github.com/dotnet/winforms/pull/12016
- [x] ItemTypeToolStripMenuItem.cs #12199
- [x] LabelDesigner.cs #10771
- [x] LinkAreaEditor.LinkAreaUI.cs https://github.com/dotnet/winforms/pull/12725
- [x] LinkAreaEditor.cs #12718
- [x] ListAdapter.cs #12093
- [x] ListBoxDesigner.cs https://github.com/dotnet/winforms/pull/11712
- [x] ListControlStringCollectionEditor.cs https://github.com/dotnet/winforms/pull/12516
- [x] ListControlUnboundActionList.cs https://github.com/dotnet/winforms/pull/12770
- [x] ListViewActionList.cs https://github.com/dotnet/winforms/pull/11782
- [x] ListViewDesigner.cs #13301
- [x] ListViewGroupCollectionEditor.cs #13275
- [x] MaskDescriptor.cs https://github.com/dotnet/winforms/pull/11703
- [x] MaskDescriptorComparer.cs https://github.com/dotnet/winforms/pull/11734
- [x] MaskDescriptorTemplate.cs https://github.com/dotnet/winforms/pull/11743
- [x] MaskDesignerDialog.cs #12575
- [x] MaskPropertyEditor.cs https://github.com/dotnet/winforms/pull/11955
- [x] MaskedTextBoxDesigner.cs #10780
- [x] MaskedTextBoxTextEditor.cs https://github.com/dotnet/winforms/pull/11737
- [x] MaskedTextBoxTextEditorDropDown.cs https://github.com/dotnet/winforms/pull/12244
- [x] MaskedTextBoxDesignerActionList.cs https://github.com/dotnet/winforms/pull/12491
- [x] MenuCommands #807
- [x] MonthCalendarDesigner.cs https://github.com/dotnet/winforms/pull/11692
- [x] NotifyIconDesigner https://github.com/dotnet/winforms/pull/11774
- [x] NotifyIconDesignerActionList #12813
- [x] OleDragDropHandler https://github.com/dotnet/winforms/pull/13022
- [x] PanelDesigner https://github.com/dotnet/winforms/pull/12113
- [x] ParentControlDesigner.cs #13173
- [x] PictureBoxActionList https://github.com/dotnet/winforms/pull/12201
- [x] PrintDialogDesigner #12117
- [x] RichTextBoxDesigner https://github.com/dotnet/winforms/pull/12061
- [x] RichTextBoxActionList https://github.com/dotnet/winforms/pull/12131
- [x] SRDisplayNameAttribute https://github.com/dotnet/winforms/pull/12169
- [ ] ScrollableControlDesigner
- [x] SelectionUIHandler #13013
- [x] SplitterDesigner https://github.com/dotnet/winforms/pull/12359
- [x] SplitterPanelDesigner https://github.com/dotnet/winforms/pull/12269
- [x] ~~StatusBarDesigner~~ StatusBar control is deprecated
- [x] ShortcutKeysEditor #1297
- [x] StandardCommandToolStripMenuItem #13215
- [x] StandardMenuStripVerb #13492
- [x] StatusCommandUI #13121
- [x] TabControlDesigner https://github.com/dotnet/winforms/pull/12130
- [x] TableLayoutPanelCodeDomSerializer #13212
- [x] TableLayoutPanelDesigner #13028
- [x] TabOrder #13181
- [x] TabPageDesigner https://github.com/dotnet/winforms/pull/12097
- [x] TemplateNodeCustomMenuItemCollection https://github.com/dotnet/winforms/pull/12035
- [x] TextBoxDesigner #12095
- [x] UpDownBaseDesigner.cs https://github.com/dotnet/winforms/pull/12364
- [x] UserControlDocumentDesigner.cs https://github.com/dotnet/winforms/pull/12710
- [x] TextBoxBaseDesigner https://github.com/dotnet/winforms/pull/12433
- [x] TextBoxActionList #12198
- [x] ToolStripActionList https://github.com/dotnet/winforms/pull/12525
- [x] ToolStripAdornerWindowService #13029
- [x] ToolStripDesignerUtils #12967
- [x] ToolStripContainerActionList #13256
- [x] ToolStripContentPanelDesigner https://github.com/dotnet/winforms/pull/12366
- [x] ToolStripContainerDesigner #12200
- [x] ToolStripDropDownDesigner #9575
- [x] ToolStripPanelDesigner #12922
- [ ] ToolStripKeyboardHandlingService #13896
- [x] ToolStripMenuItemCodeDomSerializer #12883 #13200
- [x] ToolStripInSituService #13297
- [x] ToolStripEditorManager #13218
- [x] ToolStripCollectionEditor #12962
- [x] ToolStripCustomTypeDescriptor.cs #12963
- [x] ~~WebBrowserDesigner~~ This designer has not been ported, tracking it with #9810