void markStorageNodeDown(int index) throws Exception {
            communicator.setNodeState(new Node(NodeType.STORAGE, index), State.DOWN, "foo"); // Auto-ACKed
            ctrl.tick();
        }
Class for testing states of all nodes. Will fail in constructor with
debug message on non-expected results.
clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/StateChangeTest.java