@Override
  public synchronized Page<String> listAllValidDatasets(String accountName, String containerName, String pageToken) {
    List<String> datasets = new ArrayList<>(nameToDatasetMap.get(new Pair<>(accountName, containerName)).keySet());
    Collections.sort(datasets);
    int index = 0;
    if (pageToken == null && PAGE_SIZE < 1) {
      return new Page<>(datasets, null);
    }
    if (pageToken != null) {
      index = Collections.binarySearch(datasets, pageToken);
    }
    return new Page<>(datasets.subList(index, index + PAGE_SIZE), datasets.get(index + PAGE_SIZE));
  }
Constructor.
@param shouldReturnOnlyUnknown {@code true} if always returns {@link InMemAccountService#UNKNOWN_ACCOUNT} when queried
                                                    by account name; {@code false} to do the actual query.
@param notifyConsumers {@code true} if consumers should be notified of account changes. {@code false} otherwise.
ambry-test-utils/src/main/java/com/github/ambry/account/InMemAccountService.java