private void markAsUndeleted(MockId id) {
    undeletedKeys.add(id);
    liveKeys.add(id);
    deletedKeys.remove(id);
  }
Marks {@code id} as undeleted.
@param id the {@link MockId} to mark as undeleted.
ambry-store/src/test/java/com/github/ambry/store/CuratedLogIndexState.java