Comprehensive tests

One of the issues (and one that became even more apparent during the 1.0 transistion) is that it is really hard to test this package.
Without CI development is slow since we are likely to break use-cases that we can't test.

Ideally we could use docker environments to instantiate a "minimal" cluster environment in which we then can run tests.

As an example see:
- https://github.com/giovtorres/slurm-docker-cluster