Fixes #2762. ReSharper: The same file is listed in UnitTests.csproj multiple times with the same 'Compile' build action:

[BDisp]

Fixes #2762 - Renames Checkbox.cs to CheckBox.cs, CheckboxTests.cs to CheckBoxTests.cs and CheckboxTests to CheckBoxTests class. Since the CheckBox was already changed before the file names would also justify being renamed as well as the CheckBoxTests class.

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