Is `modsim/test_modsim.py` still a valid unit test

[rioj7]

Viewing modsim/test_modsim.py in VSC with PyLance shows a lot of errors.

A lot of functions are missing.

An object can't be an instance of a function.

pint is not used, and also UnitStrippedWarning

[AllenDowney]

Yes, the test code is out of date with the current version of modsim.py