'When the process ends succesfully, the before-shutdown event is
unregistered.'

def test_unregisters_killer_success(self):

    reactor = ProcessCoreReactor()
    run(reactor, ['command', 'and', 'args'])
    [process] = reactor.processes
    process.processProtocol.processEnded(Failure(ProcessDone(0)))
    self.assertEqual(reactor._triggers['shutdown'].before, [])
