Implement some unit tests

[Vheissu]

While much of what the Shorthand Connect plugin does is simplistic (make an API request and save the values, then display them), I think it could benefit from a few simple unit tests. I've made a few changes to this plugin, and for peace of mind, I think it would be great to have some tests just to ensure everything is working as intended.

@benhoad If you wanted to assign this one to me, I would love to add in some unit tests for this plugin if you believe that it could benefit from them. Nothing too fancy, just the basics.

[benhoad]

Yeah I think any kind of testing is needed <_<
Admittedly our WP plugin hasn't got as much love as our Drupal one has of late and I'm looking to get that sorted in the next week or so.
Front of mind for me atm is addressing the file system handling and zip extraction.