Add public function unit tests

[trir262]

I added pester unit tests to functions wherever they are possible

Description

Added tests in all .tests.ps1 files

Related Issue

Motivation and Context

It allows better validation of the functions if you want to modify them.

How Has This Been Tested?

pester.ps1

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [X] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [X] I have added tests to cover my changes.
• [X] All new and existing tests passed.