'L{LogPublisher.removeObserver} removes an observer that is not
registered.'

def test_removeObserverNotRegistered(self):

    o1 = (lambda e: None)
    o2 = (lambda e: None)
    o3 = (lambda e: None)
    publisher = LogPublisher(o1, o2)
    publisher.removeObserver(o3)
    self.assertEqual(set((o1, o2)), set(publisher._observers))
