code: public boolean zoneNAryExists(int zoneId, int zoneNAry, int partitionId) {
          int currentZoneNAry = -1;
          for(int replicatingNodeId: getReplicationNodeList(partitionId)) {
              Node replicatingNode = cluster.getNodeById(replicatingNodeId);
              if(replicatingNode.getZoneId() == zoneId) {
                  currentZoneNAry++;
                  if(currentZoneNAry == zoneNAry) {
                      return true;
                  }
              }
          }
          return false;
      }
docs: TODO: add unit test.