List<String> getInstancesForPartition(String partition) {
    List<String> instances = new ArrayList<>();
    for (MockHelixAdmin helixAdmin : helixAdmins.values()) {
      instances.addAll(helixAdmin.getInstancesForPartition(partition));
    }
    return instances;
  }
Get the instances that have replicas for the given partition.
@param partition the partition name of the partition.
@return the list of instances that have replicas for this partition.
ambry-clustermap/src/test/java/com/github/ambry/clustermap/MockHelixCluster.java