@Override
  Pair<Long, NavigableMap<LogSegmentName, Long>> getValidDataSizeByLogSegment(TimeRange timeRange) {
    long deleteReferenceTimeInMs = timeRange.getEndTimeInMs();
    if (validDataSizeByLogSegments != null) {
      return new Pair<Long, NavigableMap<LogSegmentName, Long>>(deleteReferenceTimeInMs, validDataSizeByLogSegments);
    } else {
      return null;
    }
  }
Mock {@link BlobStoreStats} for test purposes
ambry-store/src/test/java/com/github/ambry/store/CompactionPolicyTest.java