Example where the test hangs after at the 48th run:
----
[haypo@freebsd ~/prog/python/2.7]$ ./python -m test -F -m test.test_threading.ConditionTests.test_notify -v test_threading 
(...)
0:00:10 [ 47] test_threading
test_notify (test.test_threading.ConditionTests) ... ok
(...)
0:00:10 [ 48] test_threading
test_notify (test.test_threading.ConditionTests) ... 
----

It looks like a timing issue / race condition since the likehood of the bug seems to depend on the system load.

Traceback using my watchdog:
https://github.com/python/cpython/pull/2317

---
0:00:57 [285] test_threading
test_notify (test.test_threading.ConditionTests) ... *** STACKTRACE - START ***
# ThreadID: 34391913984
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 37, in task
  f()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 360, in f
  cond.wait()
File: "/usr/home/haypo/prog/python/2.7/Lib/threading.py", line 340, in wait
  waiter.acquire()

# ThreadID: 34392086528
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 37, in task
  f()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 360, in f
  cond.wait()
File: "/usr/home/haypo/prog/python/2.7/Lib/threading.py", line 340, in wait
  waiter.acquire()

# ThreadID: 34384994304
File: "/usr/home/haypo/prog/python/2.7/Lib/runpy.py", line 174, in _run_module_as_main
  "__main__", fname, loader, pkg_name)
File: "/usr/home/haypo/prog/python/2.7/Lib/runpy.py", line 72, in _run_code
  exec code in run_globals
File: "/usr/home/haypo/prog/python/2.7/Lib/test/__main__.py", line 3, in <module>
  regrtest.main_in_temp_cwd()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/regrtest.py", line 2030, in main_in_temp_cwd
  main()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/regrtest.py", line 812, in main
  result = local_runtest()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/regrtest.py", line 798, in local_runtest
  testdir=testdir)
File: "/usr/home/haypo/prog/python/2.7/Lib/test/regrtest.py", line 1007, in runtest
  return runtest_inner(test, verbose, quiet, huntrleaks, pgo, testdir)
File: "/usr/home/haypo/prog/python/2.7/Lib/test/regrtest.py", line 1196, in runtest_inner
  indirect_test()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/test_threading.py", line 929, in test_main
  ThreadingExceptionTests,
File: "/usr/home/haypo/prog/python/2.7/Lib/test/support/__init__.py", line 1571, in run_unittest
  _run_suite(suite)
File: "/usr/home/haypo/prog/python/2.7/Lib/test/support/__init__.py", line 1530, in _run_suite
  result = runner.run(suite)
File: "/usr/home/haypo/prog/python/2.7/Lib/unittest/runner.py", line 151, in run
  test(result)
File: "/usr/home/haypo/prog/python/2.7/Lib/unittest/suite.py", line 70, in __call__
  return self.run(*args, **kwds)
File: "/usr/home/haypo/prog/python/2.7/Lib/unittest/suite.py", line 108, in run
  test(result)
File: "/usr/home/haypo/prog/python/2.7/Lib/unittest/suite.py", line 70, in __call__
  return self.run(*args, **kwds)
File: "/usr/home/haypo/prog/python/2.7/Lib/unittest/suite.py", line 108, in run
  test(result)
File: "/usr/home/haypo/prog/python/2.7/Lib/unittest/case.py", line 393, in __call__
  return self.run(*args, **kwds)
File: "/usr/home/haypo/prog/python/2.7/Lib/unittest/case.py", line 329, in run
  testMethod()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 401, in test_notify
  self._check_notify(cond)
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 384, in _check_notify
  _wait()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 16, in _wait
  time.sleep(0.01)

# ThreadID: 34384996864
File: "/usr/home/haypo/prog/python/2.7/Lib/threading.py", line 774, in __bootstrap
  self.__bootstrap_inner()
File: "/usr/home/haypo/prog/python/2.7/Lib/threading.py", line 801, in __bootstrap_inner
  self.run()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/regrtest.py", line 1971, in run
  self.dump_threads()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/regrtest.py", line 1997, in dump_threads
  self.dump_thread(stack)

# ThreadID: 34392083968
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 37, in task
  f()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 360, in f
  cond.wait()
File: "/usr/home/haypo/prog/python/2.7/Lib/threading.py", line 340, in wait
  waiter.acquire()

# ThreadID: 34392080128
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 37, in task
  f()
File: "/usr/home/haypo/prog/python/2.7/Lib/test/lock_tests.py", line 360, in f
  cond.wait()
File: "/usr/home/haypo/prog/python/2.7/Lib/threading.py", line 340, in wait
  waiter.acquire()

*** STACKTRACE - END ***
---