Tests for notebooks

[rajivsam]

We have tests for the basic workflow and CI. We also need a test to run the individual notebooks and examples. For notebooks, the following api to run the entire notebook and examine errors may be useful:
https://blog.thedataincubator.com/2016/06/testing-jupyter-notebooks/
So if we have refactoring changes, running the tests for the individual notebook tells you if a notebook is affected.
@joerg84 , what are your thoughts about this?