@Override
    public TopologyGraph getGraph(Topology topology) {
        return defaultTopology(topology).getGraph();
    }
@Test
    public void testGetGraph() {
        manager.registerTenantId(TenantId.tenantId(tenantIdValue1));
        VirtualNetwork virtualNetwork = manager.createVirtualNetwork(TenantId.tenantId(tenantIdValue1));
        TopologyService topologyService = manager.get(virtualNetwork.id(), TopologyService.class);
        Topology topology = topologyService.currentTopology();

        // test the getGraph() method.
        assertNotNull("The graph should not be null.", topologyService.getGraph(topology));
    }