What happened:
running the openSUSE python-distributed package build+test in a 1-core VM failed 2 tests.

distributed/tests/test_diskutils.py .....FF
test_workspace_concurrency
test_workspace_concurrency_intense

What you expected to happen:
all tests should succeed. If there are tests that do not make sense on 1 core, cpu_count() should be used to skip them.

Minimal Complete Verifiable Example:

taskset 1 pytest-3.8 distributed/tests/test_diskutils.py

Anything else we need to know?:

Environment:

• Dask version: 2.25.0
• Python version: 3.8.6
• Operating System: openSUSE-Tumbleweed 20210104
• Install method: source / rpm .spec

This bug was found while working on reproducible builds for openSUSE.