Feature/BE-43: Backend Unittests [2]

[BElifb]

• Added tests for Bidding System and Recommendation System APIs.
• 7 total for Bidding System.
• 6 total for Recommendation System.
• Tests check for multiple things, added comments about what each test checks for.
• To run all the tests python manage.py test .
• To run a single test python manage.py test -k <name_of_the_function>
• To remove results rm test-output/*

[KarahanS]

• Changed the name of the PR to be consistent with the first unittest PR we had.
• Due to the most recent bugfix and hotfix PRs, some of the previously written unit tests were not working properly. Updated those unit tests to reflect the most recent changes on our implementation.
• Also there was a print statement left in one of the Recommendation related unittests. Removed that as well. Now, it's ready to go.