'Test that advancing the clock will fire some calls.'

def testAdvance(self):

    events = []
    c = task.Clock()
    call = c.callLater(2, (lambda : events.append(None)))
    c.advance(1)
    self.assertEqual(events, [])
    c.advance(1)
    self.assertEqual(events, [None])
    self.assertFalse(call.active())
