protected ArrayListMultimap<String, ServerAndLoad>
    reconcile(ArrayListMultimap<String, ServerAndLoad> previousLoad, List<RegionPlan> plans) {
    ArrayListMultimap<String, ServerAndLoad> result = ArrayListMultimap.create();
    result.putAll(previousLoad);
    if (plans != null) {
      for (RegionPlan plan : plans) {
        ServerName source = plan.getSource();
        updateLoad(result, source, -1);
        ServerName destination = plan.getDestination();
        updateLoad(result, destination, +1);
      }
    }
    return result;
  }
Asserts a valid retained assignment plan.
<p>
Must meet the following conditions:
<ul>
<li>Every input region has an assignment, and to an online server
<li>If a region had an existing assignment to a server with the same address a a currently
online server, it will be assigned to it
</ul>
hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/RSGroupableBalancerTestBase.java