Add code coverage for toolstripComboBox

[Zheng-Li01]

related #10453

Proposed changes

Add unit tests for ToolStripComboBox to test its properties & methods & events

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.09917%. Comparing base (e4085eb) to head (e397939).
Report is 59 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #11999         +/-   ##
===================================================
+ Coverage   75.01536%   75.09917%   +0.08380%     
===================================================
  Files           3047        3064         +17     
  Lines         631584      632256        +672     
  Branches       46764       46785         +21     
===================================================
+ Hits          473785      474819       +1034     
+ Misses        154434      154062        -372     
- Partials        3365        3375         +10     

Flag	Coverage Δ
Debug	75.09917% <100.00000%> (+0.08380%)	⬆️
integration	17.94234% <ø> (+0.00794%)	⬆️
production	48.26913% <ø> (+0.14449%)	⬆️
test	97.01791% <100.00000%> (+0.00144%)	⬆️
unit	45.29529% <ø> (+0.16915%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.