Fix the ability to run network and flaky tests

[shoyer]

The old setup didn't seem to work on CI, even when we explicitly passed the
relevant flags.

[pep8speaks]

Hello @shoyer! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2019-07-04 20:02:40 UTC

[codecov]

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[max-sixty]

Hmmm, this is my code. Checking what I missed. We use the similar code internally and it works (I think...)

Do we have any flaky tests? I only see one that's marked, and that's skipped anyway (maybe because of this problem):

rg flaky      

azure-pipelines.yml
24:        pytest_extra_flags: --run-flaky --run-network-tests

setup.cfg
13:    flaky: flaky tests

conftest.py
8:    parser.addoption("--run-flaky", action="store_true",
9:                     help="runs flaky tests")
16:    if not config.getoption("--run-flaky"):
17:        skip_flaky = pytest.mark.skip(
18:            reason="set --run-flaky option to run flaky tests")
20:            if "flaky" in item.keywords:
21:                item.add_marker(skip_flaky)

doc/whats-new.rst
1847:- Enhanced tests suite by use of ``@slow`` and ``@flaky`` decorators, which are
1848:  controlled via ``--run-flaky`` and ``--skip-slow`` command line arguments

xarray/tests/__init__.py
112:flaky = pytest.mark.flaky

xarray/tests/test_plot.py
30:@pytest.mark.flaky
31:@pytest.mark.skip(reason='maybe flaky')

[shoyer]

Hmm... maybe it does work, at least in this. But we definitely aren't running the network tests, even with these changes (e.g., look at the TestPydapOnline tests). I'm not quite sure why.

[max-sixty]

--run-network works fine

 I  test  ~/w/xarray   *  pytest --run-network xarray/tests/test_tutorial.py                                                                                               192ms  Tue Jul  2 02:45:19 2019
Test session starts (platform: darwin, Python 3.7.3, pytest 4.6.3, pytest-sugar 0.9.2)
rootdir: /Users/maximilian/workspace/xarray, inifile: setup.cfg
plugins: xdist-1.29.0, forked-1.0.2, sugar-0.9.2, regtest-1.4.1, testmon-0.9.16, pycharm-0.5.0, celery-4.3.0
collecting ...
 xarray/tests/test_tutorial.py ✓✓                                                                                                                                                                100% ██████████
=============================================================================================== warnings summary ===============================================================================================
xarray/tests/test_tutorial.py::TestLoadDataset::test_download_from_github
  /usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/importlib/_bootstrap.py:219: RuntimeWarning: numpy.ufunc size changed, may indicate binary incompatibility. Expected 192 from C header, got 216 from PyObject
    return f(*args, **kwds)

xarray/tests/test_tutorial.py::TestLoadDataset::test_download_from_github
xarray/tests/test_tutorial.py::TestLoadDataset::test_download_from_github_load_without_cache
  /usr/local/lib/python3.7/site-packages/_pytest/python.py:174: RuntimeWarning: deallocating CachingFileManager(<function _open_scipy_netcdf at 0x114e29840>, '/Users/maximilian/.xarray_tutorial_data/tiny.nc', mode='r', kwargs={'mmap': None, 'version': 2}), but file is not already closed. This may indicate a bug.
    testfunction(**testargs)

-- Docs: https://docs.pytest.org/en/latest/warnings.html

Results (15.92s):
       2 passed  # <-- runs
 N  test  ~/w/xarray   *  pytest  xarray/tests/test_tutorial.py                                                                                                            17.6s  Tue Jul  2 02:49:10 2019
Test session starts (platform: darwin, Python 3.7.3, pytest 4.6.3, pytest-sugar 0.9.2)
rootdir: /Users/maximilian/workspace/xarray, inifile: setup.cfg
plugins: xdist-1.29.0, forked-1.0.2, sugar-0.9.2, regtest-1.4.1, testmon-0.9.16, pycharm-0.5.0, celery-4.3.0
collecting ...
 xarray/tests/test_tutorial.py ss                                                                                                                                                                100% ██████████

Results (3.06s):
       2 skipped  # <-- skips

[max-sixty]

Let's def change to the most reliable & standard approach here. I think I originally got this from https://docs.pytest.org/en/latest/example/simple.html#control-skipping-of-tests-according-to-command-line-option but if this is minority let's make the switch

What makes us think the existing approach wasn't working? (not saying that it did work in CI! It does seem to work locally though)

[shoyer]

Pytest reports the exact same number of tests passed, both with and without --run-network-tests. That seems suspicious to me.

[max-sixty]

That does sound suspicious! I'm on vacation with bad WiFi but let me confirm in the next few days, if that's ok

[max-sixty]

Somewhat weirdly. I get different results; could you confirm yours?

 pytest --run-network-tests

---

Results (175.99s):
    7266 passed
       5 xpassed
      19 xfailed
    1092 skipped

pytest

---

Results (165.58s):
    7264 passed
       5 xpassed
      19 xfailed
    1094 skipped

Also of note: --run-network also works, as does --run-n

[shoyer]

I'm referring to the tests running on CI, e.g., "Linux py36-flakey" on Azure. If you look at the full logs from this PR (which I made verbose) and scroll down you see:

xarray/tests/test_backends.py::TestPydapOnline::test_cmp_local_file SKIPPED [ 13%]
xarray/tests/test_backends.py::TestPydapOnline::test_compatible_to_netcdf SKIPPED [ 13%]
xarray/tests/test_backends.py::TestPydapOnline::test_dask SKIPPED        [ 13%]
xarray/tests/test_backends.py::TestPydapOnline::test_session SKIPPED     [ 13%]

So for some reason it's not doing flakey tests, even though in theory I'm passing the right flags for it:

xarray/ci/azure/unit-tests.yml

Line 14 in 681ec0e

--cov-report=html $EXTRA_FLAGS

Actually, I definitely screwed this up. I should be using $PYTEST_EXTRA_FLAGS, not $EXTRA_FLAGS. Let me try fixing that...