Replace deprecated, unmaintained nose with another solution

[mbrukman]

As noted in our GitHub Actions config, we had to exclude Python 3.10 and 3.11 due to nose incompatibility that will not be fixed, so we need to migrate to another option (nose2 or pytest):

ipycache/.github/workflows/master.yml

Lines 16 to 23 in ca8a1fb

	# Tests running via `nosetests` on Python 3.10 fail with the error:
	#
	# "AttributeError: module 'collections' has no attribute 'Callable'"
	#
	# Per https://github.com/nose-devs/nose/issues/1099, nose is no longer
	# maintained and so this will not be fixed; we need to migrate to either
	# nose2 or pytest, per the discussion on the above issue.
	python: [ '3.7', '3.8', '3.9' ]

However, nosetests appears to have been removed in the GitHub Actions images for Ubuntu and macOS, as evidenced by this failure with Python 3.8 on ubuntu-18.04:

Run nosetests
/home/runner/work/_temp/1b158be5-bebc-467e-a8c7-2491044116ae.sh: line 1: nosetests: command not found
Error: Process completed with exit code 127.

We see similar failures with Python (3.8, 3.9) on Ubuntu (18.04, 20.04) and macOS (10.15, 11).

Although we can probably quick-fix this with pip install nose or adding it to test_requirements.txt, we might as well use this opportunity to instead migrate to a newer tool to enable us to test with newer Python versions as well.

[jakirkham]

pytest is also used by a lot of projects. Maybe another option to consider. This doc on migrating from nose may help

[mbrukman]

Thanks, @jakirkham! Will take a look at this later; right now, just trying to do a quick fix in #63 so that we can unblock the license clarification fix.

[mbrukman]

@jakirkham — I looked at the tests, and it seemed much easier to port them to Python standard library unittest (which I'm very familiar with) than to rewrite using either nose2 or pytest. This also lets us remove an extra test dependency, which will (hopefully) speed up our automated testing pipeline as well. I'll submit a PR shortly to fix this.