Historically, we've used nose as the test runner, with a custom test

runner script responsible for setting up a Django environment for the

given version of Django.
Unfortunately, nose 1.x hasn't been updated in a long while, and isn't

compatible with modern versions of Python 3. The forks also don't

support Python 3 very well. nose2 does, but is so different that it's

not a great option for us.
Instead, we're moving to pytest. This is a much more modern test

runner with a lot of interesting capabilities and a wide ecosystem of

plugins.
We now use this and define all our custom setup logic using pytest

hooks in conftest.py. This handles Django setup, and adds a --db

option for specifying which test database we want to use to run the

suite.
Developers can now run pytest directly to run the test suite. The old

./tests/runtests.py still works, but is deprecated, and merely wraps

pytests anyway.

Tested with manual test runs, using a variety of parameters.
Ran the whole Python/Django compatibility matrix using tox. All

tests passed.