Add information about additional helpful pytest features

[bielsnohr]

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In the course of a run of the course at UKAEA, the following feedback was collected:

• Recommend adding ids argument to pytest.parameterise, e.g. else you can have a test my_test[1-2-None] which is not very informative.
• Explaining how to run one sub-test (encourage quotes for cross-shell compatibility - zsh doesnt like without):

  pytest -k "my_test[iteration-name]"
  

• Mention other useful opts?
  • -s stdout
  • -x terminate on first fail
  • -v show each test by name

@kzscisoft I believe it might have been you to add this? Anything further you might add?

The usual concern is adding more material to an already lengthy course. However, perhaps this could be added as an "Optional" exercise for learners that are a little bit ahead?