add support for backend tests.

[WilliamDormer]

Create a new tests folder and follow tutorials/documentation to add mocha/chai testing (or a different framework if you have a strong preference). The purpose of this is to allow us to test out some of our most complex endpoints more quickly and as a unit with clear inputs and outputs (looking at you, profile put, and swipe put). Plus it is good practice to have tests that we can run before production to ensure that the quality of the code is good and there are no logical errors. This may require restructuring the project slightly, so if you get blocked by that, let me know and change the issue label to help wanted.