private boolean isSystemTableIsolated(BalancerClusterState cluster) {
    return isTableIsolated(cluster, SYSTEM_TABLE_NAME, "System");
  }
If your minCostNeedsBalance is set too low, then the balancer should still eventually stop making
moves as further cost improvements become impossible, and balancer plan calculation becomes
wasteful. This test ensures that the balancer will not get stuck in a loop of continuously moving
regions.
hbase-balancer/src/test/java/org/apache/hadoop/hbase/master/balancer/TestUnattainableBalancerCostGoal.java