@Override
    public IndexBlockEncoding getIndexBlockEncoding() {
      return NoOpIndexBlockEncoder.INSTANCE.getIndexBlockEncoding();
    }
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