Add Unit Tests

[growdev]

Overview

This issue includes adding a method for running unit tests on the code to make sure new functionality does not introduce bugs in existing functionality.

Description

Testing will be added using PHPUnit since it is the testing framework chosen by the core team.

A composer file will be added to handle managing required packages and defining scripts for testing.

Tasks

• Add composer.json.
• Add phpunit.xml.
• Add setup script
• Add bootstrap file.
• Add tests for functions in Add Custom Schedule #13 #14.