Fixed -- Doc'd fix for test suite hang on macOS.
@@ -380,6 +380,20 @@ 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.
+On **macOS** (High Sierra and newer versions), you might see this message
+logged, after which the tests hang::
+
+ objc[42074]: +[__NSPlaceholderDate initialize] may have been in progress in
+ another thread when fork() was called.
+
+To avoid this set a ``OBJC_DISABLE_INITIALIZE_FORK_SAFETY`` environment
+variable, for example::
+
+ $ OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES ./runtests.py
+
+Or add ``export OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES`` to your shell's
+startup file (e.g. ``~/.profile``).
+
Many test failures with ``UnicodeEncodeError``
----------------------------------------------
