Make requirements, test requirements more explicit; add [test] pip extra

[ryan-williams]

(factored out of #612)

[savingoyal]

@ryan-williams If you can address the comment in the PR, we can merge this in.

[ryan-williams]

just rebased and addressed the comment, gonna try to resuscitate a few of these, thanks for your patience

[ryan-williams]

Just rebased this, not sure what this failure in "R tests on macos-latest" is about:

==> Pouring checkbashisms--2.21.7.all.bottle.tar.gz
installer: Package name is gfortran
installer: Installing at base path /
installer: The install was successful.
/usr/bin/sudo hdiutil detach /Volumes/gfortran-8.2-Mojave
hdiutil: couldn't unmount "disk2" - Resource busy
Error: Failed to get R 4.1.1: Failed to get R 4.1.1: Failed to umount /Volumes/gfortran-8.2-Mojave: Error: The process '/usr/bin/sudo' failed with exit code 16
🍺  /usr/local/Cellar/checkbashisms/2.21.7: 6 files, 72.2KB

[ryan-williams]

I think the above was a spurious failure, fwiw; I tweaked this PR once more to alphabetize requirements-test.txt, mostly just to get the CI to run again, and it passed.

So, this should be ready for another look if anyone has time.

[ryan-williams]

thanks @savingoyal 🙏 looks like this is good to merge?

[romain-intel]

LGTM

[nflx-mf-bot]

Testing[44] @ 5da5e67

[nflx-mf-bot]

Testing[44] @ 5da5e67

[nflx-mf-bot]

Testing[44] had 3 FAILURES.

[ryan-williams]

Not sure how to parse "Testing[44] had 3 FAILURES." above. Where does that CI run?

[romain-intel]

@ryan-williams : I am using your PR as a guinea pig for some tests we run internally. The CI is not accessible so don't worry about the message (it's a good comment though -- I will modify the message to indicate that the message can be ignored mostly). As you can see, it's not yet fully working (it worked fine when using branches from this repo but not so much from a fork (yet)).