Add code coverage for ToolStripSplitButton

[Zheng-Li01]

related #10453

Proposed changes
Add unit tests for ToolStripSplitButton.cs 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 75.43926%. Comparing base (0d0e1c9) to head (554ff00).
Report is 11 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #12238         +/-   ##
===================================================
+ Coverage   75.42712%   75.43926%   +0.01214%     
===================================================
  Files           3102        3102                 
  Lines         634244      634472        +228     
  Branches       46866       46880         +14     
===================================================
+ Hits          478392      478641        +249     
+ Misses        152434      152417         -17     
+ Partials        3418        3414          -4     

Flag	Coverage Δ
Debug	75.43926% <100.00000%> (+0.01214%)	⬆️
integration	17.98261% <ø> (+0.00303%)	⬆️
production	48.81450% <ø> (+0.01080%)	⬆️
test	97.02802% <100.00000%> (+0.00177%)	⬆️
unit	45.81943% <ø> (-0.01645%)	⬇️

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[LeafShi1]

If the target of the test is the constructor, you must ensure that the corresponding constructor is called. From the current test, only the Image property is tested, Other test cases also have this problem.
so this test here should like following,

using Bitmap image1 = new Bitmap(10, 10);
_toolStripSplitButton = new("Test", image);

_toolStripSplitButton.SupportsSpaceKey.Should().BeTrue();
_toolStripSplitButton.Image.Should().Be(image);

int defaultDropDownButtonWidth = _toolStripSplitButton.TestAccessor().Dynamic.DefaultDropDownButtonWidth;
_toolStripSplitButton.DropDownButtonWidth.Should().Be(defaultDropDownButtonWidth);

_toolStripSplitButton = new("Test", image: null);
_toolStripSplitButton.Image = null;
_toolStripSplitButton.Image.Should().BeNull();
_toolStripSplitButton.DropDownButtonWidth.Should().Be(defaultDropDownButtonWidth);

The above example needs to be optimized

[Tanya-Solyanik]

If the target of the test is the constructor, you must ensure that the corresponding constructor is called.

This test is testing constructor with 2 arguments, not the default one that you call on line 16 in the test class constructor.
In this case we want to dispose button allocated on line 16 and then initialize that field using constructor that takes 2 arguments

_toolStripSplitButton.Dispose();
_toolStripSplitButton = new("Test", image);

In other tests, that validate properties, we are guaranteed that the default constructor is called before the Fact runs. There is no need to execute it twice in other Facts.

[LeafShi1]

LGTM with a little question

[LeafShi1]

Extra space

[Tanya-Solyanik]

Suggested change

	toolStripSplitButton.Text.Should().BeEmpty();
	_toolStripSplitButton.Text.Should().BeEmpty();

I don't think you have to invoke constructor because we are guaranteed that it is called, we can test properties of our field.

[Tanya-Solyanik]

If the target of the test is the constructor, you must ensure that the corresponding constructor is called.

This test is testing constructor with 2 arguments, not the default one that you call on line 16 in the test class constructor.
In this case we want to dispose button allocated on line 16 and then initialize that field using constructor that takes 2 arguments

_toolStripSplitButton.Dispose();
_toolStripSplitButton = new("Test", image);

In other tests, that validate properties, we are guaranteed that the default constructor is called before the Fact runs. There is no need to execute it twice in other Facts.