Add test coverage for MaskedTextBox

[MelonWang1]

Related #10453

Proposed changes

• Add unit tests for MaskedTextBox to test its properties: BeepOnError, AsciiOnly and Culture

Customer Impact

• None

Regression?

• No

Risk

• Minimal

Test methodology

• Unit tests

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.20584%. Comparing base (bd97476) to head (c5922ee).
Report is 45 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #10978         +/-   ##
===================================================
+ Coverage   73.17333%   73.20584%   +0.03250%     
===================================================
  Files           3097        3097                 
  Lines         633955      634448        +493     
  Branches       47364       47380         +16     
===================================================
+ Hits          463886      464453        +567     
+ Misses        166522      166448         -74     
  Partials        3547        3547                 

Flag	Coverage Δ
Debug	73.20584% <100.00000%> (+0.03250%)	⬆️
integration	18.44236% <ø> (-0.00840%)	⬇️
production	46.71475% <ø> (+0.04067%)	⬆️
test	94.97323% <100.00000%> (-0.00132%)	⬇️
unit	43.61802% <ø> (+0.07276%)	⬆️

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[Tanya-Solyanik]

@LeafShi1, @SimonZhao888 , @Epica3055 , @ricardobossan - please review this PR

[ricardobossan]

Maybe add tests for default values, to prevent unwanted changes in behavior. Like:

[WinFormsFact]
public void MaskedTextBox_DefaultValues()
{
    var control = new MaskedTextBox();

    Assert.False(control.AcceptsTab);
    Assert.True(control.AllowPromptAsInput);
    Assert.False(control.AsciiOnly);
    Assert.False(control.BeepOnError);
    Assert.False(control.CanUndo);
}

[ricardobossan]

We are moving towards adopting Fluent Assertions for tests. Take inspiration from these recent commits:

• Commit 1: Simple assertions
• Commit 2: Exception assertions

For a detailed guide, refer to the Fluent Assertions documentation here.

[ricardobossan]

LGTM