Move tests to py.test

[yuvipanda]

Currently most of notebook/tests (except the selenium ones) are all using the built-in unittest module. Native pytest format tests (with just functions) feels more readable and better adopted now. We also use it a lot in other parts of the ecosystem.

How do people feel about moving?

[mpacer]

An additional step would be to remove the nose test dependencies as well. It's designed around extending unittest oriented testing suites and it would likely enable switching to pytest based testing.

Also nose has not been actively developed for a while, from their website

Nose has been in maintenance mode for the past several years and will likely cease without a new person/team to take over maintainership.

[minrk]

Personally, I'd vote for new tests to be written that way if they can, but it might not be worth the effort to migrate a large and complicated test base to it.

[mpacer]

I think part of the challenge with that is that without fixtures already in place for some of the functionality, it becomes hard to even write new test without needing to rebuild the entire underlying infrastructure.

One thought: It might make sense to take one existing test that we think will require making the appropriate fixtures and then migrate that & create those fixtures, so that new tests can build upon that basis.

[mcepl]

Given nose is going to be incompatible with upcoming version of Python (certainly 3.10), here is the patch we use in OpenSUSE to eliminate the dependency.

[bnavigator]

#5826