'When function passed to L{TimerService} returns a deferred that errbacks,
the exception is logged, and L{TimerService.stopService} doesn\'t raise an error.'

def test_failedCallLogsError(self):

    self.timer.startService()
    self.deferred.errback(Failure(ZeroDivisionError()))
    errors = self.flushLoggedErrors(ZeroDivisionError)
    self.assertEqual(1, len(errors))
    d = self.timer.stopService()
    self.assertIdentical(self.successResultOf(d), None)
