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test.support.import_module() catchs ModuleNotFoundError instead of ImportError since the following changeset:
changeset: 84106:c4d7228421df
user: Brett Cannon <brett@python.org>
date: Wed Jun 12 20:12:30 2013 -0400
files: Lib/test/regrtest.py Lib/test/support.py Lib/test/test___all__.py Lib/xmlrpc/server.py Lib/zipfile.py
description:
Move test___all__ over to unittest.main() and use ModuleNotFoundError
The problem is that multiprocessing.synchronize raises an ImportError if _multiprocess.SemLock does not exist:
# Try to import the mp.synchronize module cleanly, if it fails
# raise ImportError for platforms lacking a working sem_open implementation.
# See issue 3770
try:
 from X_multiprocessing import SemLock
except (ImportError):
 raise ImportError("This platform lacks a functioning sem_open" +
 " implementation, therefore, the required" +
 " synchronization primitives needed will not" +
 " function, see issue 3770.")
As a result, test_multiprocessing is no more skipped on FreeBSD 6.4, but the following traceback is written:
http://buildbot.python.org/all/builders/x86%20FreeBSD%206.4%203.x/builds/3771/steps/test/logs/stdio
Re-running test 'test_multiprocessing' in verbose mode
test test_multiprocessing crashed -- Traceback (most recent call last):
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/multiprocessing/synchronize.py", line 27, in <module>
 from _multiprocessing import SemLock
ModuleNotFoundError: cannot import name SemLock
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/test/regrtest.py", line 1300, in runtest_inner
 the_module = importlib.import_module(abstest)
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/importlib/__init__.py", line 93, in import_module
 return _bootstrap._gcd_import(name[level:], package, level)
 File "<frozen importlib._bootstrap>", line 1614, in _gcd_import
 File "<frozen importlib._bootstrap>", line 1595, in _find_and_load
 File "<frozen importlib._bootstrap>", line 1562, in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 609, in _check_name_wrapper
 File "<frozen importlib._bootstrap>", line 1058, in load_module
 File "<frozen importlib._bootstrap>", line 928, in load_module
 File "<frozen importlib._bootstrap>", line 274, in _call_with_frames_removed
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/test/test_multiprocessing.py", line 30, in <module>
 test.support.import_module('multiprocessing.synchronize')
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/test/support.py", line 123, in import_module
 return importlib.import_module(name)
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/importlib/__init__.py", line 93, in import_module
 return _bootstrap._gcd_import(name[level:], package, level)
 File "<frozen importlib._bootstrap>", line 1614, in _gcd_import
 File "<frozen importlib._bootstrap>", line 1595, in _find_and_load
 File "<frozen importlib._bootstrap>", line 1562, in _find_and_load_unlocked
 File "<frozen importlib._bootstrap>", line 609, in _check_name_wrapper
 File "<frozen importlib._bootstrap>", line 1058, in load_module
 File "<frozen importlib._bootstrap>", line 928, in load_module
 File "<frozen importlib._bootstrap>", line 274, in _call_with_frames_removed
 File "/usr/home/db3l/buildarea/3.x.bolen-freebsd/build/Lib/multiprocessing/synchronize.py", line 32, in <module>
 " function, see issue 3770.")
ImportError: This platform lacks a functioning sem_open implementation, therefore, the required synchronization primitives needed will not function, see issue 3770.

Brett: Why did you close this issue? It still occurs on the buildbot:
http://buildbot.python.org/all/builders/x86%20FreeBSD%206.4%203.x/builds/3794/steps/test/logs/stdio 

Because I removed ModuleNotFoundError; check the buildbot again and you will notice it is 8 changesets behind, most of which are related to the removal of ModuleNotFoundError.