Test notebooks using testbook or delete TODO comment

[jezsadler]

Per test_run_notebooks.py, line 15:

# TODO @cog-imperial: These will be replaced with stronger tests using testbook soon

We should either replace the tests or delete the TODO.

[rmisener]

Hi @carldlaird, this is a TODO of yours from a couple years ago. Can we just delete this or move to the discussions? Or is this important and we should get someone on it? Just looking for context.