Add unit tests for ToolStripContainerDesigner

[Olina-Zhang]

Related #10773

Proposed changes

• Add unit test ToolStripContainerDesignerTests.cs for public properties and method of the ToolStripContainerDesigner.
• Enable nullability in ToolStripContainerDesignerTests.cs.

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

Attention: Patch coverage is 94.82759% with 3 lines in your changes missing coverage. Please review.

Project coverage is 75.44071%. Comparing base (99d42a9) to head (f90d22c).
Report is 43 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #12200         +/-   ##
===================================================
+ Coverage   75.26640%   75.44071%   +0.17430%     
===================================================
  Files           3086        3103         +17     
  Lines         633636      634322        +686     
  Branches       46839       46870         +31     
===================================================
+ Hits          476915      478537       +1622     
+ Misses        153316      152356        -960     
- Partials        3405        3429         +24     

Flag	Coverage Δ
Debug	75.44071% <94.82759%> (+0.17430%)	⬆️
integration	17.97802% <ø> (-0.04330%)	⬇️
production	48.83175% <ø> (+0.25932%)	⬆️
test	97.02589% <94.82759%> (+0.00186%)	⬆️
unit	45.86519% <ø> (+0.25613%)	⬆️

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[lonitra]

Suggested change

	public void Initialize_ShouldSetShadowProperties()
	{
	AssertShadowProperties("TopToolStripPanelVisible", _toolStripContainer.TopToolStripPanelVisible);
	AssertShadowProperties("LeftToolStripPanelVisible", _toolStripContainer.LeftToolStripPanelVisible);
	AssertShadowProperties("RightToolStripPanelVisible", _toolStripContainer.RightToolStripPanelVisible);
	AssertShadowProperties("BottomToolStripPanelVisible", _toolStripContainer.BottomToolStripPanelVisible);
	}
	private void AssertShadowProperties(string propertyName, object expectedValue)
	{
	var property = typeof(ToolStripContainerDesigner).GetProperty(propertyName, BindingFlags.NonPublic | BindingFlags.Instance);
	var actualValue = property?.GetValue(_designer);
	actualValue.Should().Be(expectedValue);
	}
	public void Initialize_ShouldSetShadowProperties()
	{
	AssertShadowProperties("TopToolStripPanelVisible", _toolStripContainer.TopToolStripPanelVisible);
	AssertShadowProperties("LeftToolStripPanelVisible", _toolStripContainer.LeftToolStripPanelVisible);
	AssertShadowProperties("RightToolStripPanelVisible", _toolStripContainer.RightToolStripPanelVisible);
	AssertShadowProperties("BottomToolStripPanelVisible", _toolStripContainer.BottomToolStripPanelVisible);
	void AssertShadowProperties(string propertyName, object expectedValue)
	{
	var property = typeof(ToolStripContainerDesigner).GetProperty(propertyName, BindingFlags.NonPublic | BindingFlags.Instance);
	var actualValue = property?.GetValue(_designer);
	actualValue.Should().Be(expectedValue);
	}
	}