'mock' package missing in requirements.txt

[MarinBernard]

Hi,

FYI, unit tests require the presence of the 'mock' package, which is not specified in requirements.txt.

[jperville]

Hello @MarinBernard since python 3.3 MagicMock is part of the standard library ( see https://docs.python.org/3/library/unittest.mock.html ). I prepared a PR to make the tests run even on systems without the mock library installed in the systemwide packages.