@Test
    public void testStorageCluster() {
        HostName hostName1 = new HostName("host1");
        HostName hostName2 = new HostName("host2");
        HostName hostName3 = new HostName("host3");

        ServiceCluster serviceCluster = modelUtils.createServiceCluster(
                "cluster",
                ServiceType.STORAGE,
                List.of(
                        modelUtils.createServiceInstance("storage-1", hostName1, ServiceStatus.UP),
                        modelUtils.createServiceInstance("storage-2", hostName2, ServiceStatus.DOWN)
                )
        );


        ApplicationInstance applicationInstance = modelUtils.createApplicationInstance(new ArrayList<>());
        serviceCluster.setApplicationInstance(applicationInstance);

        ClusterApiImpl clusterApi = new ClusterApiImpl(
                applicationApi,
                serviceCluster,
                new NodeGroup(applicationInstance, hostName1, hostName3),
                new HostInfos(),
                modelUtils.getClusterControllerClientFactory(),
                ModelTestUtils.APPLICATION_PARAMS.clusterParamsFor(serviceCluster),
                clock);

        assertTrue(clusterApi.isStorageCluster());
        assertEquals(Optional.of(hostName1), clusterApi.storageNodeInGroup().map(storageNode -> storageNode.hostName()));
    }
Make a ClusterApiImpl for the cfg1 config server, with cfg3 missing from the cluster (not provisioned).
orchestrator/src/test/java/com/yahoo/vespa/orchestrator/model/ClusterApiImplTest.java