pytest migration: model: convert all tests to TestControllerPytest The model tests were based on BaseTestCase which does not exist currently for pytest-style tests. Nevertheless, there seems to be no advantage of directly subclassing BaseTestCase over subclassing TestControllerPytest. Thus, keep things simple and use TestControllerPytest.

# requirements.txt file for use as "pip install -r requirements.txt" as a
# readthedocs compatible alternative to "pip install -e ." which is a working
# alternative to "setup.py develop" which doesn't work with Mercurial 3.7
.