Create basic backend tests

[eveninglily]

Having tested code can be extremely helpful in validating that it is correct, and new changes don't break existing behavior. Right now, we don't have any tests for the backend.

Setup a test file, and test a few of the endpoints - make sure they return the expected status code and other output

Useful links:

• https://flask.palletsprojects.com/en/1.1.x/testing/
• https://realpython.com/python-mock-library/ (This lets us mock objects, so we can just pretend a function (i.e. database call) returns something)

[eveninglily]

This might require another docker-compose config to work smoothly - I'll try to take care of that to not block this task