Use unittest.mock on Python 3

[hroncok]

In Fedora, we would like to get rid of the separately packaged mock package.

[mgedmin]

LGTM!

(I'm fine with dropping any Python < 3.6 support at this point, so this could be made simpler and use unittest.mock exclusively.)

[mgedmin]

Ugh, isort is dumb and doesn't understand that import sections wrapped in try/except are import sections (one blank line of separation) instead of two (which is what I want between the last import section and the beginning of actual code).

Options:

• fix isort (hard, unrealistic)
• add the extra blank line isort demands (ugly, acceptable)
• change isort configuration in setup.cfg (lines_after_imports = 1 instead of 2), but this causes breakage for other Python files
• drop import mock and always use unittest.mock (probably the best solution, but extra work needed in dropping Python 2.7 first)

Oh hey I see I already dropped Python < 3.6 support for this package, so all the conditional for-python-before-3.3 dependencies are kind of pointless anyway! EDIT: oops I checked the wrong package! But it's past time to drop 2.7 here too.

Let's go with "always use unitttest.mock".

[mgedmin]

extra work needed in dropping Python 2.7 first

and since it would be unfair to pile that work onto you, I've created #63, which, incidentally also drops the mock dependency.

[hroncok]

extra work needed in dropping Python 2.7 first

and since it would be unfair to pile that work onto you, I've created #63, which, incidentally also drops the mock dependency.

Thank you for being this nice!