Create Unit Tests using `unittest`

[rvare]

There should be a set of unit tests to check for correctness of the program. This should be done using Python's unittest library (which is part of the Python standard library and so we don't need to add any packages to it). These should be put in the test/ folder.

We should test for the following:

• Arguments work as they should,
• Conversions work as they should,
• Error handling,
• Test any assert statements in the code,
• Any edge cases we can come up with.

Comment to this issue if you think of any other cases that should be tested.