Add Unit tests using pytest

[skafai]

The code is well documented, but it lacks testing and therefore it would be very useful to implement unit tests using pytest.

The aim is to have 100% coverage, so any contributions are welcome.

[mnajibi]

Hi there, can I work on this issue?

[skafai]

Hi there, can I work on this issue?

@mnajibi Thank you! Feel free to fork the repo and open a pull request as soon as you are done.