reproduce this behaviour using docker and docker-compose by running
$ docker-compose build
[...]
$ docker-compose run web python manage.py test
Creating test database for alias 'default'...
....
----------------------------------------------------------------------
Ran 4 tests in 0.153s
OK
Destroying test database for alias 'default'...
$ docker-compose run web python manage.py test --settings mysite.fast_tests
Creating test database for alias 'default'...
....
----------------------------------------------------------------------
Ran 4 tests in 0.002s
OK
Destroying test database for alias 'default'...
fast_tests removes the ldapdb.backends.ldap database backend, which makes tests significantly faster.
Notes:
- there is not a single code or tests which is acually using python-ldapdb
- speed slows down liniar with the number of tests, so slow down is not because of initial test overhead