Am seeing the test distributed/tests/test_client.py::test_futures_of_class failing on CI. This started happening recently. The error is a bit peculiar

elif dask.is_dask_collection(x):
[1314](https://github.com/dask/distributed/runs/6329112229?check_suite_focus=true#step:11:1314)
>               stack.extend(x.__dask_graph__().values())
[1315](https://github.com/dask/distributed/runs/6329112229?check_suite_focus=true#step:11:1315)
E               TypeError: Array.__dask_graph__() missing 1 required positional argument: 'self'

Not sure, but maybe this is related to PR ( dask/dask#8674 )

cc @douglasdavis @dask/maintenance (in case anyone has ideas 🙂)

Yea I think it's related to changing is_dask_collection in dask/dask#8674.

In the test futures_of is getting one element list where the element is the class da.Array, not an instance. In is_dask_collection we now check for the attribute __dask_graph__ and see if it's callable. Perhaps we should also check to make sure that the thing (x) that has a callable __dask_graph__ is an instance and not a class.

With dask/dask#9054 the test passes

Unit Test Results

       12 files  +       12         12 suites  +12   5h 28m 34s ⏱️ + 5h 28m 34s
  2 760 tests +  2 760    2 665 ✔️ +  2 665    92 💤 +  92  3 ❌ +3 
16 534 runs  +16 534  15 730 ✔️ +15 730  796 💤 +796  8 ❌ +8 

For more details on these failures, see this check.

Results for commit 159aeb9. ± Comparison against base commit 9f7646a.

Looks like things are working again with the Dask fix. Thanks Doug! 🙏