Add unit tests

[sara-02]

Add unit tests to test different features of BENJI.
Some may require mocking data(if they are talking to external APIS)
Resources to get started with testing in Python:

1. https://jeffknupp.com/blog/2013/12/09/improve-your-python-understanding-unit-testing/
2. https://www.geeksforgeeks.org/unit-testing-python-unittest/

[Pradhvan]

I can take this up @sara-02

Just one question why use the Unit test module? , if possible we should move to PyTest it makes testing a bit more Pythonic 😄