easyrsa unit tests fail on Py35

[Cory Johns]

https://github.com/charmed-kubernetes/layer-easyrsa/pull/32/checks?check_run_id=1806071711

Seems like actual test failures but I'm not sure why it only applies to Python 3.5.

Also, Nick pointed out that Python 3.5 is deprecated in the current pip and pip 21 will drop support entirely. I think we have to continue to support Python 3.5 as long as we support Xenial, so we may need to do something to ensure that an older version of pip is used for those tests.

[Martin Kalcok (martin-kalcok)]

re: test failures
The log from the github CI run is unfortunately expired, but I ran the tests on the xenial machine with python 3.5 and the problem is that the tests use `Mock.assert_called` method [1] which was added python 3.6. I currently work on UT coverage of easyrsa layer, so I can include fix for this in the same PR.
Additionally, I'll propose change to github actions so that the tests are run on all opened PRs, not only on push to `master` branch, so that these problems can be caught before PR merge.

re: python35
I think this is fine as long as the github actions we use, support python 3.5. We don't have much control over which pip is used. We just specify on which python interpreters we want to run our tests.

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[1] https://docs.python.org/3/library/unittest.mock.html?highlight=mock#unittest.mock.Mock.assert_called

[Kevin W Monroe (kwmonroe)]

This appears fixed by the work done in coverage bug lp:1901687. Marking dupe.