private MockId getIdToTtlUpdate(Set<MockId> ids) {
    MockId updateCandidate = null;
    for (MockId id : ids) {
      if (liveKeys.contains(id) && !ttlUpdatedKeys.contains(id)
          && allKeys.get(id).getFirst().getExpirationTimeInMs() != Utils.Infinite_Time) {
        updateCandidate = id;
        break;
      }
    }
    if (updateCandidate == null) {
      throw new IllegalStateException("Could not find a key to update in set: " + ids);
    }
    ttlUpdatedKeys.add(updateCandidate);
    return updateCandidate;
  }
Gets an id to update TTL for from {@code ids} by picking the first live key that has a non-infinte TTL encountered.
@param ids the {@link MockId}s to choose from
@return an id to update from {@code ids}
ambry-store/src/test/java/com/github/ambry/store/BlobStoreTest.java