[Systemroles] how to pylint and pytest storage role python code?

[Rich Megginson]

I'm trying to convert the storage role to use tox.  I'm getting errors 
like this running pylint and pytest:

pylint:

************* Module find_unused_disk
E: 67, 0: No name 'size' in module 'ansible.module_utils' 
(no-name-in-module)
E: 67, 0: Unable to import 'ansible.module_utils.size' (import-error)

pytest:

Traceback:
unit/test_unused_disk.py:2: in <module>
     import find_unused_disk
../library/find_unused_disk.py:67: in <module>
     from ansible.module_utils.size import Size
E   ImportError: No module named size

How do you run pytest?  Do you have to set PYTHONPATH?