void waitForSystemStateVersion(int version, Duration timeout) {
        try {
            Instant endTime = Instant.now().plus(timeout);
            while (getLatestSystemStateVersion().orElse(-1) < version) {
                if (Instant.now().isAfter(endTime))
                    throw new RuntimeException("Timed out waiting for state version " + version + " in " + this);
                Thread.sleep(10);
            }
        } catch (InterruptedException e) { /* ignore */ }
    }
History of received cluster states.
Any access to this list or to its members must be synchronized on the timer variable.
clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/DummyVdsNode.java