Review Bot 4 is using the nose-based test runner on Review Board 5 and

higher. This isn't as good an experience, compared to pytest, and

doesn't work on newer versions of Python at all. We also intended to

remove nose support entirely in Review Board 7, and though we didn't do

that, its time is coming.
We now opt into pytest-based support. This just requires that we have a

conftest.py invoking our test plugin. Versions of rbext that support

pytest will notice this and invoke pytest instead of nose.

Unit tests pass on all supported versions of Python.