private StoreFindToken getTombstoneToken(int index) throws Exception {
    if (index >= state.permanentDeleteTombstones.size()) {
      return null;
    }

    MockId tombstone = state.permanentDeleteTombstones.get(index);
    IndexValue deleteIndexValue = state.index.findKey(tombstone);
    IndexSegment indexSegment = state.index.getIndexSegments().floorEntry(deleteIndexValue.getOffset()).getValue();
    // find a key that is behind tombstone
    IndexSegment segmentBehindSegment =
        state.index.getIndexSegments().higherEntry(indexSegment.getStartOffset()).getValue();
    MockId keyInToken1 = (MockId) segmentBehindSegment.iterator().next().getKey();
    StoreFindToken peerToken =
        new StoreFindToken(keyInToken1, segmentBehindSegment.getStartOffset(), state.sessionId, state.incarnationId,
            segmentBehindSegment.getResetKey(), segmentBehindSegment.getResetKeyType(),
            segmentBehindSegment.getResetKeyLifeVersion());
    return peerToken;
  }
Get the store token behind the tombstone
@return the store token behind the tombstone
ambry-store/src/test/java/com/github/ambry/store/BlobStoreCompactorTest.java