'L{_ContinuousPolling.removeAll} removes all descriptors and returns
the readers and writers.'

def test_removeAll(self):

    poller = _ContinuousPolling(Clock())
    reader = object()
    writer = object()
    both = object()
    poller.addReader(reader)
    poller.addReader(both)
    poller.addWriter(writer)
    poller.addWriter(both)
    removed = poller.removeAll()
    self.assertEqual(poller.getReaders(), [])
    self.assertEqual(poller.getWriters(), [])
    self.assertEqual(len(removed), 3)
    self.assertEqual(set(removed), set([reader, writer, both]))
