public Set<String> getKeySetToDownload(Set<String> blobStoreKeySet, Set<String> zookeeperKeySet) {
        zookeeperKeySet.removeAll(blobStoreKeySet);
        LOG.debug("Key list to download {}", zookeeperKeySet);
        return zookeeperKeySet;
    }
@Test
  public void testBlobSynchronizerForKeysToDownload() {
    BlobStore store = initLocalFs();
    LocalFsBlobStoreSynchronizer sync = new LocalFsBlobStoreSynchronizer(store, conf);
    // test for keylist to download
    Set<String> zkSet = new HashSet<>();
    zkSet.add("key1");
    Set<String> blobStoreSet = new HashSet<>();
    blobStoreSet.add("key1");
    Set<String> resultSet = sync.getKeySetToDownload(blobStoreSet, zkSet);
    assertTrue(resultSet.isEmpty(), "Not Empty");
    zkSet.add("key1");
    blobStoreSet.add("key2");
    resultSet =  sync.getKeySetToDownload(blobStoreSet, zkSet);
    assertTrue(resultSet.isEmpty(), "Not Empty");
    blobStoreSet.remove("key1");
    blobStoreSet.remove("key2");
    zkSet.add("key1");
    resultSet =  sync.getKeySetToDownload(blobStoreSet, zkSet);
    assertTrue((resultSet.size() == 1) && (resultSet.contains("key1")), "Unexpected keys to download");
  }