One useful clue: when I run these tests on OS X, I get the following warnings: ``` ========================================= warnings summary ========================================== xarray/tests/test_distributed.py::test_dask_distributed_integration_test[scipy] /Users/shoyer/conda/envs/xarray-py36/lib/python3.6/site-packages/distributed/utils_test.py:528: UserWarning: This test leaked 8 file descriptors warnings.warn("This test leaked %d file descriptors" % diff) /Users/shoyer/conda/envs/xarray-py36/lib/python3.6/site-packages/distributed/utils_test.py:538: UserWarning: This test leaked 15 MB of memory warnings.warn("This test leaked %d MB of memory" % diff)

xarray/tests/test_distributed.py::test_dask_distributed_integration_test[netcdf4] /Users/shoyer/conda/envs/xarray-py36/lib/python3.6/site-packages/distributed/utils_test.py:528: UserWarning: This test leaked 6 file descriptors warnings.warn("This test leaked %d file descriptors" % diff)

-- Docs: http://doc.pytest.org/en/latest/warnings.html ```

This is Python 2.7.14.

We do have a build against git master for dask, but only on Linux (Appveyor only gives us one free simultaneous build).

Comparing a failed build to the last successful build on master, I find the following difference in the dependencies: ```

passed, just before the v0.10.0 release

ca-certificates 2017.7.27.1 0 conda-forge dask 0.15.4 py_0 conda-forge dask-core 0.15.4 py_0 conda-forge distributed 1.19.3 py27_0 conda-forge setuptools 36.6.0 py27_1 conda-forge

failed, at the v0.10.0 release

ca-certificates 2017.11.5 0 conda-forge dask 0.16.0 py_0 conda-forge dask-core 0.16.0 py_0 conda-forge distributed 1.20.0 py27_0 conda-forge setuptools 36.7.2 py27_0 conda-forge `` It looks like dask 0.16 or distributed 0.1.20 release is the most likely culprit. There were no Python changes to xarray in the v0.10.0 release commit (onlysetup.py` and documentation changes).

It definitely started recently (past week). I don't think we changed anything relevant in xarray so my guess is something to do with a dependency. Hopefully it will be clear from the appveyor logs! On Wed, Nov 22, 2017 at 4:49 PM Matthew Rocklin notifications@github.com wrote:

If I may generalize the question, did this start happening recently? Do we know what triggered this change?

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It looks like it, I'll double check.

On Wed, Nov 22, 2017 at 4:46 PM Matthew Rocklin notifications@github.com wrote:

At first glance, no. Does this happen both on latest release and on git-master?

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