Add unit tests for the package

[nialov]

Problem

There is no way to verify that the package works without some kind of test framework that can be run after installation.

Solution

I suggest starting with a few simple tests for the validate_enc and check_file functions. pytestseems reasonable as the test runner.

Let me know if you want me to make a pull request for this! I would add pytest to setup.py test_requires dependencies and draft a few simple tests that check a valid and invalid file at the very least.

[yuvipanda]

Yes, would love to have a PR with some tests! Thank you so much!