Missing fixture when using distributed.utils_test.client fixture in pytest

What happened:

When attempting to use the distributed.utils_test.client in a test suite for one of my packages, my tests error out due to a missing fixture loop that is required by the client fixture. The traceback is pasted below in the MCVE.

What you expected to happen:

To be able to use the client fixture without raising an error when running tests that require a distributed.Client instance.

Minimal Complete Verifiable Example:

from distributed.utils_test import client


def test_foo(client):
    def inc(x):
        return x + 1
    foo = client.submit(inc, x)

when running this as,

pytest test-dask-client-fixture.py (where I’ve put the above snippet in a file called dask-client-fixture.py), I get the following error message from pytest,

======================================================= test session starts ========================================================
platform darwin -- Python 3.8.5, pytest-6.2.2, py-1.10.0, pluggy-0.13.1
rootdir: /Users/wbarnes/Desktop
collected 1 item

test-dask-client.py E                                                                                                        [100%]

============================================================== ERRORS ==============================================================
____________________________________________________ ERROR at setup of test_foo ____________________________________________________
file /Users/wbarnes/Desktop/test-dask-client.py, line 4
  def test_foo(client):
file /Users/wbarnes/miniconda3/envs/dask-fresh/lib/python3.8/site-packages/distributed/utils_test.py, line 543
  @pytest.fixture
  def client(loop, cluster_fixture):
E       fixture 'loop' not found
>       available fixtures: cache, capfd, capfdbinary, caplog, capsys, capsysbinary, client, doctest_namespace, monkeypatch, pytestconfig, record_property, record_testsuite_property, record_xml_attribute, recwarn, tmp_path, tmp_path_factory, tmpdir, tmpdir_factory
>       use 'pytest --fixtures [testpath]' for help on them.

/Users/wbarnes/miniconda3/envs/dask-fresh/lib/python3.8/site-packages/distributed/utils_test.py:543
===================================================== short test summary info ======================================================
ERROR test-dask-client.py::test_foo
========================================================= 1 error in 5.25s =========================================================

Environment:

• Dask version: 2021.1.1
• Python version: 3.8.5
• pytest version: 6.2.2
• Operating System: macOS 10.15.3 (I’ve also encountered this on Ubuntu 18.04.5)
• Install method (conda, pip, source): pip

[jrbourbeau]

Hmm in that case, you might be best off creating your own fixture where you set the scope= keyword in pytest.fixture. For example, something along the lines of (haven’t tested the snippet below at all):

from distributed import LocalCluster

@pytest.fixture(scope="session")
def test_cluster():
    with LocalCluster() as cluster:
        yield cluster

[jrbourbeau]

Sounds good. Good luck @wtbarnes!