@Override
    public TopologyCluster getCluster(Topology topology, ClusterId clusterId) {
        checkNotNull(clusterId, CLUSTER_ID_NULL);
        return defaultTopology(topology).getCluster(clusterId);
    }
@Test
    public void testGetCluster() {
        VirtualNetwork virtualNetwork = setupVirtualNetworkTopology();

        TopologyService topologyService = manager.get(virtualNetwork.id(), TopologyService.class);
        Topology topology = topologyService.currentTopology();

        Set<TopologyCluster> clusters = topologyService.getClusters(topology);
        assertNotNull("The clusters should not be null.", clusters);
        assertEquals("The clusters size did not match.", 2, clusters.size());

        // test the getCluster() method.
        TopologyCluster cluster = clusters.stream().findFirst().get();
        assertNotNull("The cluster should not be null.", cluster);
        TopologyCluster cluster1 = topologyService.getCluster(topology, cluster.id());
        assertNotNull("The cluster should not be null.", cluster1);
        assertEquals("The cluster ID did not match.", cluster.id(), cluster1.id());
    }