void bringInstanceDown(String instanceName) {
    MockHelixAdmin helixAdminForInstance = null;
    for (MockHelixAdmin helixAdmin : helixAdmins.values()) {
      if (helixAdmin.getInstancesInCluster(clusterName).contains(instanceName)) {
        helixAdmin.bringInstanceDown(instanceName);
        helixAdminForInstance = helixAdmin;
        break;
      }
    }
    if (isAggregatedViewUsed) {
      localHelixAdmin.triggerLiveInstanceChangeNotification();
    } else {
      if (helixAdminForInstance != null) {
        helixAdminForInstance.triggerLiveInstanceChangeNotification();
      }
    }
  }
Bring the given instance down.
@param instanceName the instance to be brought down.
ambry-clustermap/src/test/java/com/github/ambry/clustermap/MockHelixCluster.java