add support for unit testing

[thescientist13]

after #14 / #15 / #16 and that multiple projects are now starting to rely on this API, should probably get some test cases worked into this project. Just something straight forward like mock and a couple sinon mocks, just to prevent still stuff from happening.

For any interested in contributing, I can help by getting the testing tooling setup so the focus can just be on test writing.