tests: migrate to pytest

[Sigmanificient]

Hi, nixpkgs (nixOS package repository) contributer here. nose is abandoned upstream, so in a effort of cleanup, the following set of patches were made to your project. This migrate to pytest with is a widely used python testing library.

https://nose.readthedocs.io/en/latest/

Nose has been in maintenance mode for the past several years and will likely cease without a new person/team to take over maintainership. New projects should consider using Nose2, py.test, or just plain unittest/unittest2.