Ensure that all WinForms controls have unit tests coverage for public APIs

[Tanya-Solyanik]

• Investigate if we can re-enable code coverage on internal builds
  We enabled it in Establish Code Coverage for WinForms testing #514, however Coverage option is disabled in the build pipeline -

  winforms/eng/pipelines/build.yml

  Line 33 in 95e83ed

  _Coverage: false

  .
• Generate list of controls with missing test coverage for public methods
• Work with @Olina-Zhang's team on adding the missing scenarios

[paul1956]

@Olina-Zhang @Tanya-Solyanik I don't think the VB code has much test coverage. I added some in my yet to be merged PR #9867. I was not able to add anything for Network Uploads as I have no idea how to access a server to upload to.

[Tanya-Solyanik]

@paul1956 - good point about the missing VB-specific coverage. We'll add it after the C# coverage is in done.

[SimonZhao888]

Following controls are missing test coverage for public methods:
System.Windows.Forms

• Button Add code coverage for buttons #10693
• CheckBox Add code coverage for buttons #10693, Add test coverage for checkbox #11249
• FlatButton Add code coverage for buttons #10693
• RadioButton Add code coverage for buttons #10693, Add unit tests for RadioButton and RadioButton.RadioButtonAccessibleObject #11687
• ComboBox Add test coverage for ComboBox #11381, Add test coverage for ComboBox #11533, Add code coverage for combobox #11565, Add code coverage for comboBox #11699, Add code coverage for comboBox #12038
• DataGridView Add unit test case for DataGridView 10 events #11541, Add unit test case for DataGridView 16 events #11556, Add unit test case for DataGridView 7 events #11618, Add unit test case for DataGridView 21 events #11691
• DateTimePicker Add test coverage for DateTimePicker #11033, Updated the BackColorChanged and BackgroundImageChanged event test cases in DateTimePickerTest.cs #11106, Add unit test for DateTimePicker 6 events #11318, Add unit test for DateTimePicker 12 properties #11385, Updated 6 unit test cases to fully coverage code lines in DateTimePicker #11534, Add unit test for DateTimePicker 8 events #11463
• GroupBox Add unit tests for GroupBox #11688
• Label Add unit tests for Label #10787, Add test coverage for Label  #10976, Add code coverage for LabelAccessibleObject #11521
• LinkLabel
• CheckedListBox Add unit test for checkedListBox #11265, Add unit test for CheckedListBox.CheckedIndexCollection #11317,
  Add test coverage for CheckedListBox.CheckedItemCollection and CheckedIndexCollection #11384, Add unit tests for CheckedListBox and CheckedListBox.CheckedListBoxItemAccessibleObject #11647
• ListBox Add test coverage for ListBox #11624, Add code coverage for ListBoxAccessibleObject and ListBoxItemAccessib… #11724
• ListView Add code coverage for ListView #11264, Add test coverage for ListView #11380, Add test coverage for ListView #11701
• MenuStrip
• MonthCalendar Add code coverage for MonthCalendar #11149, Add code coverage for MonthCalendar #11217, Add code coverage for monthcalendar #11519, Add code coverage for monthcalendar #11619
• ProgressBar Add code coverage for ProgressBarRenderer #11074
• PropertyGrid Add test coverage for PropertyGrid #11476, Add test coverage for PropertyGrid #11587, Add test coverage for PropertyGrid.PropertyTabCollection #11711
• RichTextBox Add code coverage for RichTextBox #10994
  Add code coverage for RichTextBox #10921
  Add code coverage for RichTextBox #11034
• MaskedTextBox Add test coverage for MaskedTextBox #10978, Add test coverage for MaskedTextBox #11231, Add test coverage for MaskedTextBox #11286, Add test coverage for MaskedTextBox #11376
• TextBox Add test coverage for TextBox #11021
• ToolStrip Add Code Coverage For ToolStrip #11464, Add code coverage for ToolStripTextBox #11848, Add code coverage for toolstrip #11773, Add code coverage for ToolStripTextBox #11848, Add code coverage for ToolStripMenuItem #11887, Add code coverage for ToolStripPanel_ToolStripPanelRowCollection #12111, Add code coverage for ToolStripSplitStackDragDropHandler #12082, Add code coverage for toolStripStatusLabel #12043, Add code coverage for toolstripComboBox #11999, Add code coverage for ToolStripMenuItem #11887, Add code coverage for ToolStripSplitButton #12238, Add code coverage for ToolStripLabel.cs file #12166
• TrackBar Add unit test for TrackBar #11066, Add test coverage for TrackBar Accessible Object #11397
• TreeView Add test coverage for TreeView #11293, Add test coverage for TreeView #11361, Add code coverage for treeview #11686
• DomainUpDown Add unit tests for DomainUpDown #11331
• WebBrowser Add test case for WebBrowserBase #10755
• NumericUpDown Add test coverage for NumericUpDown #11522