Create unit tests for backend constraints logic

[joshRamirez]

Overview

We need to write unit tests so that functionality is not broken across updates to this fundamental piece of logic. This will also help us define how we intend for this logic to work!

Action Items

Mostly research now.
How do we properly structure the test classes?
How do we mock the sqlalchemy objects?
What are the expected response data for both candidates and locations?
What are the expected outcomes?

Resources/Instructions

These libraries are already included in python so we would not need to add dependencies.
https://docs.python.org/3/library/unittest.html
https://docs.python.org/3/library/unittest.mock.html