public static HostName getControllerHostName(ApplicationInstance application, ClusterId contentClusterId) {
        //  It happens that the master Cluster Controller is the one with the lowest index, if up.
        return getClusterControllerInstancesInOrder(application, contentClusterId).stream()
                .findFirst()
                .orElseThrow(() ->
                        new IllegalArgumentException("No cluster controllers found in application " + application));
    }
@Test
    public void testGetControllerHostName() {
        HostName host = VespaModelUtil.getControllerHostName(application, CONTENT_CLUSTER_ID);
        assertEquals(controller0Host, host);
    }