private void addServiceInstances(List<ServiceInstance> list, ServiceStatus status, int num) {
        for (int i = 0; i < num; ++i) {
            ServiceInstance service = mock(ServiceInstance.class);
            when(service.serviceStatus()).thenReturn(status);
            list.add(service);
        }
    }
Tests automatic failing of nodes.

@author bratseth
@author mpolden
node-repository/src/test/java/com/yahoo/vespa/hosted/provision/maintenance/NodeFailerTest.java