support custom test runners

[matthewleon]

Currently, pytest runs the setup_databases methods from Django's DiscoverRunner to set up the database. It should support setup_databases from custom test runners as defined in the TEST_RUNNER setting.

[javrasya]

+1 for me.

[pelme]

pytest-django does not use Django's DiscoverRunner for running the tests - pytest is the test runner and that is the entire purpose of pytest-django.

In fact, DiscoverRunner is not even used by pytest-django in Django 1.6+ if you look carefully in https://github.com/pytest-dev/pytest-django/blob/master/pytest_django/compat.py

However, the problem of not being able to swap setup_databases to something different remains, but this will be solved with pytest fixtures. See #37 (comment) for an example on this. When such fixtures can be defined, it will be trivial to the appropriate methods from another test runner class.

Closing this issue since custom test runners cannot be supported in this way.