'Any existing configuration is wiped by ``/configuration/_compose``.'

def test_overwrite_existing(self):

    application = Application(name=u'myapp', image=DockerImage.from_string(u'busybox'), running=False)
    dataset = Dataset(dataset_id=unicode(uuid4()))
    manifestation = Manifestation(dataset=dataset, primary=True)
    saved = self.persistence_service.save(Deployment(nodes=[Node(uuid=uuid4(), applications={application.name: application}, manifestations={manifestation.dataset_id: manifestation})]))
    saved.addCallback((lambda _: self.configuration_test()))
    return saved
