Add modin tests

[ckw017]

Why are these changes needed?

Adds modin tests that run with and without ray client. For reviewers: most of test_modin.py is copied from modin's unit tests that cover basic dataframe operations. The parts added in to run with ray client are in this section.

Currently we need to install a commit from modin's master branch, since one of the fixes that gets it to work with client isn't in a release yet. We can change this to be modin >= 0.10 once its released.

Related issue number

Covers ray's end of modin-project/modin#3085

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[amogkam]

Can you make sure that test_modin is run in the CI? You’d have to add it to one of the build files. You can probably just follow the same as what’s being done for dask.

Also cc @rkooo567

[rkooo567]

Btw how are these tests written? Did we copy from the modin repo?

[ckw017]

Yup, they're from here, details are in the license bit at the top of the file and in LICENSE

[ckw017]

Oh hmm, do we only run tests on Python 3.6 for linux? The latest versions of Modin only run on 3.7+ because of a pandas dependency. It's passing on the Windows runs though, which uses 3.7

[ckw017]

@amogkam Added test_modin to medium tests k to z, and added a skip for what looks like an incorrectly written test in test_mldataset, which I can open an issue for

[AmeerHajAli]

@amogkam , can you please rereview this?

[amogkam]

Nice work @ckw017! This looks really good, but it looks like the test isn't actually being run in the CI right now due to the Python version. I left some comments to address.

Also, @rkooo567, would be great if you could take a look at this as well.

[ckw017]

@amogkam made the changes, I'm keeping the updated modin dependency in the the main requirements.txt since it looks like the travis and build kite runs still try to run test_modin as part of Small & Large with 3.6 and 3.7, which would error out because of modin's strict ray versioning requirements if we don't enforce >= 0.10

[amogkam]

LGTM! Please ping when tests pass

[ckw017]

@amogkam Good to go!