Add unit tests for ParentControlDesigner

[MelonWang1]

Related #10773

Proposed changes

• Add unit test ParentControlDesignerTests.cs for public properties and method of the ParentControlDesigner.

Microsoft Reviewers: Open in CodeFlow

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Codecov Report

Attention: Patch coverage is 93.61702% with 9 lines in your changes missing coverage. Please review.

Project coverage is 61.87079%. Comparing base (4d44901) to head (ba4a5c8).
Report is 81 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13173         +/-   ##
===================================================
+ Coverage   61.35261%   61.87079%   +0.51818%     
===================================================
  Files           1547        1553          +6     
  Lines         158479      159088        +609     
  Branches       14751       14816         +65     
===================================================
+ Hits           97231       98429       +1198     
+ Misses         60545       59943        -602     
- Partials         703         716         +13     

Flag	Coverage Δ
Debug	61.87079% <93.61702%> (+0.51818%)	⬆️
integration	10.72448% <ø> (-0.00005%)	⬇️
production	39.89668% <ø> (+0.67483%)	⬆️
test	95.66556% <93.61702%> (-0.01391%)	⬇️
unit	37.34492% <ø> (+0.68645%)	⬆️

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Pull Request Overview

This pull request adds unit tests for ParentControlDesigner to validate its public properties and methods.

• Introduces ParentControlDesignerTests.cs with tests for snap lines, control parenting, glyph retrieval, and component initialization.
• Covers scenarios such as valid snap line collection, handling of null default values, and reparenting controls when applicable.

Comments suppressed due to low confidence (2)

src/System.Windows.Forms.Design/tests/UnitTests/System/Windows/Forms/Design/ParentControlDesignerTests.cs:39

• [nitpick] Consider caching the cast of snapLines to a List in a local variable to improve readability and avoid repeated casts in the assertions.

((List<SnapLine>)snapLines).Should()

src/System.Windows.Forms.Design/tests/UnitTests/System/Windows/Forms/Design/ParentControlDesignerTests.cs:144

• [nitpick] Hiding the base method 'Contains' with 'new' might be confusing for future maintainers; consider overriding the method or renaming this implementation to clarify its intent.

public new bool Contains(Control ctl)

[ricardobossan]

Thank you!

[Tanya-Solyanik]

Added one comment

[Tanya-Solyanik]

THank you!