You need to additionally establish the testing requirements :
pip install -r tests/requirements.txt
This will install the mock package and solve the no module named mock in Python 2 (assuming you install it in the same environment from which you are running the tests).
Note that to run the tests you must use tox (which will also install the missing dependencies from requirements.txt during the test run setup phase):
tox -- tests/test_loader.py
(itβs just that all and the tests are executed and passed to me).
FYI, here is my PyCharm configuration for talk runner:

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