Unit testing

[remykusters]

It would be good to design some simple unit tests (we could use the examples that are currently present on the website) to see if every commit does not unintentionally impact anything in the code.

[GJBoth]

See #28

[GijsVermarien]

I think that the test cases that are in examples could be a good starting point, these could be tests for the package functionality as a whole.