WIP: Rewrite tests

Use unit tests for testing Python code.

We do not want to test the data, only the Python code. So this commit provides some dummy known good fake data.

Tests can be run with the following command:

PYTHONPATH=$PWD/lib/python python2 -m pytest lib/python/tests

Do people agree with this approach?

Are the old tests still useful for testing the data? Based on the errors I got I suspect nobody is using them...