@Override
    public Collection<AmbryDisk> getDisks(AmbryDataNode dataNode) {
      if (dataNode != null) {
        return dataNodeToDisks.getOrDefault(dataNode, Collections.emptySet());
      }
      List<AmbryDisk> disksToReturn = new ArrayList<>();
      for (Set<AmbryDisk> disks : dataNodeToDisks.values()) {
        disksToReturn.addAll(disks);
      }
      return disksToReturn;
    }
A helper class that mocks the {@link ClusterManagerQueryHelper} and stores partition to replicas mapping internally
as told.
ambry-clustermap/src/test/java/com/github/ambry/clustermap/DynamicClusterManagerComponentsTest.java