logilab-common #8100 pytest seems to be 6 to 9 times slower than unittest [deprecated]

For a given module containing tests, pytest seems to be 6 to 9 times slower than the unittest module (my test machine is crater). I have writen a script 'frameworks_comparison.py' for reproducing the problem, you can run it by:

python frameworks_comparison.py

This script will create two modules made of tests and make a comparison between the two frameworks. You can also run evaluations yourself by:

time pytest test_pytest.py
time python test_unittest.py

I would be interested of an execution time at most 2 times slower for this given case where the test module is supplied. Would it be possible to add this behavior with an option? Did I miss a point somewhere? I will definitly make a blog explaining how to run the tests faster once the problem solved.