Add PHP Unit testing

[ProfessorTom]

As a Developer, I would like to have unit tests for the PHP code in this site/application to:

• [ ] Prove that code meets expectations
• [ ] Make code more modular
• [ ] Make refactoring code a low-risk event

[ProfessorTom]

I’ve not written any unit tests in PHP before, but am aware that PHPUnit is a thing.

While I expect I will likely be the one to add PHPUnit or its equivalent to this project, I am leaving this task unassigned for now until I have more confidence in my ability to add a PHP unit testing framework and some example PHP unit tests.