Skip tests relying on absent optional/external libaries

Describe the issue Arviz is meant to use/interact with external libraries that are optional, found in requirements-external.txt, requirements-optional.txt, with tests found in /tests/external-tests/. I’d propose making these tests optional when the other libraries aren’t installed, so someone not touching those areas could run tests locally without installing all the packages.

Suggested change In pyjanitor we support the use of some optional, external libraries and skip tests if the libraries can’t be loaded.

I propose modifying the test files to something like this:

try:
    import emcee
except ImportError:
    emcee= None

@pytest.mark.skipif(emcee is None, reason="emcee tests only required for CI")
def some_emcee_test():

CI should still run as is, but it’d be a bit easier for new people to get involved and test without the external libraries.

One issue with this is at least once instance with this (for pyro at least) is when a skipif decorator is also checking for pyro.version which will cause an error when it is None etc.

[hectormz]

Yes it did (from my perspective). You can close this now if it works for you.

[hectormz]

@OriolAbril I wasn’t aware of that skip, is that built into pytest? nice!

I was looking into the pytest.mark.skipif documentation and found there is an option to skip tests based on missing a dependency: pytest.importorskip

Assuming that our tests for external libraries are in separate files, this might work well. In test_data_pyro.py, the imports

import torch
import pyro
from pyro.infer import Predictive

can be replaced with

torch = pytest.importorskip("torch")
pyro = pytest.importorskip("pyro")
Predictive = pytest.importorskip("pyro.infer.Predictive")

I believe the whole file will be skipped if one of those imports fails. No other decorators need to be added to the classes/tests. I think this minimal code change is ideal, as long as the changes to imports are clear/commented well, and pylint is silenced about no longer seeing these imports as imports.