use unittest.mock instead of mock

[pgajdos]

Could you please consider to use unittest.mock at least as a fallback, when mock is not installed?

[dvzrv]

Hi! I package this project for Arch Linux and would also very much like to see this happen. We are currently trying to remove the use of mock from our packages, as since python 3.3 unittest.mock is a thing.

Is the compatibility outside of what Python upstream supports (currently >= 3.7) required for anything? It strikes me as odd to still support python 2.7 or anything below 3.7 after such a long time of it being unsupported. Is this intentional?

[dvzrv]

@xolox ping