test_threading failed on AMD64 Windows8.1 Refleaks 3.x, the unittest errors are missing, but unraisable exceptions look similar:
https://buildbot.python.org/all/#/builders/80/builds/646

0:21:11 load avg: 7.30 [156/419/3] test_threading failed (2 min 56 sec) -- running: test_concurrent_futures (7 min 40 sec), test_email (1 min 34 sec)
beginning 6 repetitions
123456
.....Warning -- Unraisable exceptionWarning -- Unraisable exception

Exception ignored in thread started byException ignored in thread started by: : <function Bunch.__init__.<locals>.task at 0x000000C7CAC57AF0><function Bunch.__init__.<locals>.task at 0x000000C7CAC57AF0>

Traceback (most recent call last):
Traceback (most recent call last):
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\test\lock_tests.py", line 41, in task
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\test\lock_tests.py", line 41, in task
    f()    
f()  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\test\lock_tests.py", line 939, in f

  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\test\lock_tests.py", line 939, in f
    i = barrier.wait()    
i = barrier.wait()  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\threading.py", line 620, in wait

  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\threading.py", line 620, in wait
    self._wait(timeout)
      File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\threading.py", line 660, in _wait
self._wait(timeout)
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\threading.py", line 660, in _wait
    raise BrokenBarrierError
threading.    BrokenBarrierErrorraise BrokenBarrierError: 

threading.BrokenBarrierError: 
Warning -- Unraisable exception
Exception ignored in thread started by: <function Bunch.__init__.<locals>.task at 0x000000C7CAC57AF0>
Traceback (most recent call last):
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\test\lock_tests.py", line 41, in task
    f()
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\test\lock_tests.py", line 939, in f
    i = barrier.wait()
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\threading.py", line 611, in wait
    self._enter() # Block while the barrier drains.
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\threading.py", line 635, in _enter
    raise BrokenBarrierError
threading.BrokenBarrierError: 
Warning -- Unraisable exception
Exception ignored in thread started by: <function Bunch.__init__.<locals>.task at 0x000000C7CAC57AF0>
Traceback (most recent call last):
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\test\lock_tests.py", line 41, in task
    f()
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\test\lock_tests.py", line 939, in f
    i = barrier.wait()
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\threading.py", line 611, in wait
    self._enter() # Block while the barrier drains.
  File "D:\buildarea\3.x.ware-win81-release.refleak\build\lib\threading.py", line 635, in _enter
    raise BrokenBarrierError
threading.BrokenBarrierError: 
test test_threading failed -- multiple errors occurred; run in verbose mode for details