Migrate from nose to a different unittest provider

[bpblanken]

the new v03 pipeline is using nose because that's what the v02 pipeline was using. However, it's not being maintained:

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](https://github.com/nose-devs/nose2), [py.test](http://pytest.org/), or just plain unittest/unittest2.

and fell over itself when pushing to python 3.10.

I've historically used py.test but a discussion and/or evaluation of other options is probably warranted.

[jklugherz]

I've been writing a lot of new nose tests lately and am very interested in migrating to pytest!

[bpblanken]

yours if you'd like it!