'``VolumeScript.main`` returns a ``Deferred`` on success.'

def test_deferred_result(self):

    script = VolumeManagerScript()
    options = VolumeOptions()
    options['config'] = FilePath(self.mktemp())
    dummy_reactor = object()
    result = script.main(dummy_reactor, options, Service())
    self.assertIs(None, self.successResultOf(result))
