Write edge case tests for '/bars' endpoint

[cadams8238]

Basic tests are set up for all CRUD operations on /bars endpoint. Test cases for edge cases need to be written for greater code coverage.

Examples:
GET /bars/:id

1. When id is not valid Mongo ObjectId
2. When id does not exist

POST /bars

1. When a required properties are not included

DELETE /bars/:id

1. When id is not valid Mongo ObjectId
2. When id does not exist

And any other edge cases you can think of! :)