Get a python module going including unit tests

investigation.py is getting cumbersome. Time to encapsulate further
logic in classes. And I might as well get a module/application going at
the same time (including unit testing).

[This is my first Python app. So it has been a bit frustrating working
out the correct folder structure, how modules work, how to define
classes and how to get unit tests running. But, considering my
inexperience, it has actually gone relatively quickly and smoothly.
Python continues to impress me!]