Setup testing and added base tests

[FalseHonesty]

Description

In this PR, I have added the base needed for writing tests in this project. This includes a testing framework, as well as a mocking library to allow us to write tests easily. Tests are important for numerous reasons, and there are any number of sources on Google that can cover why more eloquently than I can, so I encourage you to read those.

There are two new dependencies required for this, however, they do not need to be included in the packaged JAR. They are:

• JUnit5. JUnit is pretty much the de facto testing framework for the JVM.
• MockK. MockK is a very popular mocking library for Kotlin specifically, and it provides a lot of power that other libraries can't, such as the ability to mock objects.

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)

[CoalCoding]

Huge fan of this, will benefit the client a lot.

[FalseHonesty]

I've found this blog post, and I have found it to be a very good resource on some best practices for writing these tests. I believe that we should try to follow these goals in our test suite.