In Review Board 6, the pytest fixtures were moved into

reviewboard.testing.pytest_fixtures. This caused pytest to have to

import reviewboard.testing on load. The problem there is that this

module forward-imports reviewboard.testing.testcase.TestCase, and this

module depends on a working Django environment first. That causes a

crash for pytest help output or operations that don't require setting up

a test environment.
We now lazily-import TestCase in this module so that we only pull it

in when explicitly requested. This is done through a module-level

__getattr__ (available in all supported versions of Python).
A TYPE_CHECKING-level import is done to ensure that importers see the

right type for this class.

Unit tests pass on Python 3.8-3.11.
I can run pytest --help without a crash.