A test suite is needed

This project is starting to actually have traction, so it's time for us to start writing some tests for functionality. This is a placeholder issue to discuss what should have tests, what framework we should use, et cetera.

[211217613]

How about starting with basic unittest using unittest. Then maybe parameterized test with pytest and using docker, docker-compose for a testing environment.

[211217613]

How about some automated testing and CI?