It means one less file to manage. If we want this to work, it should
be in puppet anyways.

No critical change, but some wording review, splitting in sections and
more links

We're gaining a month every day these days, congrats weasel!

 * failure to import pytest doesn't need to be tested
 * plt.show() can't be tested non-interactively
 * the "if main" wrapper is essentially untestable and otherwise covered

for some reason, I cannot reproduce the backtrace micah had, so the
check code is never triggered.