For example, with test2Clusters:

Traceback (most recent call last):
  File "neo/master/app.py", line 111, in run
    self._run()
  File "neo/master/app.py", line 131, in _run
    self.playPrimaryRole()
  File "neo/master/app.py", line 318, in playPrimaryRole
    self.provideService()
  File "neo/master/app.py", line 269, in provideService
    em.poll(1)
  File "neo/lib/event.py", line 90, in poll
    self._poll(timeout=timeout)
  File "neo/tests/threaded/__init__.py", line 150, in _poll
    Serialized.tic(self._lock)
  File "neo/tests/threaded/__init__.py", line 102, in tic
    cls.release(lock); cls.acquire(lock)
  File "neo/tests/threaded/__init__.py", line 88, in acquire
    elif threading.currentThread() in cls.pending:
TypeError: argument of type 'int' is not iterable