private String do_test_distribution_bit_watermark(int lowestObserved, int node0MinUsedBits) {
        final ClusterFixture fixture = ClusterFixture.forFlatCluster(3)
                .bringEntireClusterUp()
                .reportStorageNodeState(0, new NodeState(NodeType.STORAGE, State.UP).setMinUsedBits(node0MinUsedBits));

        final ClusterStateGenerator.Params params = fixture.generatorParams()
                .highestObservedDistributionBitCount(8) // TODO is this even needed for our current purposes?
                .lowestObservedDistributionBitCount(lowestObserved);

        return ClusterStateGenerator.generatedStateFrom(params).toString();
    }
Cluster-wide distribution bit count cannot be higher than the lowest split bit
count reported by the set of storage nodes. This is because the distribution bit
directly impacts which level of the bucket tree is considered the root level,
and any buckets caught over this level would not be accessible in the data space.
clustercontroller-core/src/test/java/com/yahoo/vespa/clustercontroller/core/ClusterStateGeneratorTest.java