Add unit tests

[DrySoldier]

We need to maintain ten lines of "Hello World!" and the only way to ensure that is unit tests. Please implement.

[fmbearmf]

Need to make sure it's production ready

[floppydisken]

We should really be abstracting the IO operations, so that the functionality can be unit tested. Also, is anyone working on integration tests?

[karmalegend]

Please also add a mutation test report so there is a way to validate the quality of said unit/integration tests.