FileSpan addUndeleteEntry(MockId idToUndelete) throws StoreException {
    return addUndeleteEntry(idToUndelete, null, MessageInfo.LIFE_VERSION_FROM_FRONTEND);
  }
Adds a undelete entry in the index (real and reference) for {@code idToUndelete}.
@param idToUndelete the id to be undeleted.
@return the {@link FileSpan} of the added entries.
@throws StoreException
ambry-store/src/test/java/com/github/ambry/store/CuratedLogIndexState.java