@Override
    public void saveMetadata(Writer writer) throws IOException {
      NoOpIndexBlockEncoder.INSTANCE.saveMetadata(writer);

    }
This test is for HBASE-27940, which midkey metadata in root index block would always be ignored
by {@link BlockIndexReader#readMultiLevelIndexRoot}.
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestHFileBlockIndex.java