Test docu: Missing docu about test_packags.py and processPackage()

[buhtz]

Just an example while I was investigating failing unit test in context of PR #722.

pydoctor/pydoctor/test/test_packages.py

Line 9 in 662eafa

def processPackage(packname: str, systemcls: Callable[[], model.System] = model.System) -> model.System:

This is not a support question. I would like to have a in code docu.
What is unclear to me:

• What is the purpose of the file test_packages.py? Might it be helper code in context of unit tests or are these tests? Or is this one of the pytest specific features I don't know about? A module doc string would help to clear this up.
• The purpose of processPackage() is also unclear. A docstring would help.
• The function docstring problem is also relevant for all other functions in this file.