Evaluate pytest-postgresql or pytest-pgsql

[ewjoachim]

Currently, our own test code takes care of setting up the db and dropping it, etc.

I wonder if https://pypi.org/project/pytest-postgresql/ or https://pytest-pgsql.readthedocs.io/en/latest/ could help. The first one looks simpler, the second supports transacted tests out of the box, which might help speeding up tests.

BTW, re-reading #238 (comment) : tests still takes 67s on my computer. That's not unbearable but if we have a simple speedup possible, that also allowed deleting code, I'm in!

This is not urgent or anything.