Add mocha unit test framework

[LucianBuzzo]

Includes a basic test file, mainly as an example and a jumping-off point

change-type: minor

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Contributor checklist

• Build output been rebuilt and tested
• Introduces security considerations
• Tests are included
• Documentation is added or changed
• Affects the development, build or deployment processes of the component

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[pimterry]

You shouldn't need this - I think if you just remove it everything should work without...

[LucianBuzzo]

That's what I thought as well, but there are some issues with ts-node not picking up @types declarations with this combination of TS and mocha.
TypeStrong/ts-node#271
I tried a few different options, and this was the cleanest solution, I'd like to come back and resolve this in the future though.

[hedss]

Hurrah!