Added note to check Python version in unit tests troubleshooting section.
At DjangoCon US 2019 sprints, a number of contributors hit problems with an outdated Python.
@@ -373,6 +373,13 @@ in ``tests/auth_tests``.
Troubleshooting
===============
+Test suite hangs or shows failures on ``master`` branch
+-------------------------------------------------------
+
+Ensure you have the latest point release of a :ref:`supported Python version
+<faq-python-version-support>`, since there are often bugs in earlier versions
+that may cause the test suite to fail or hang.
+
Many test failures with ``UnicodeEncodeError``
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