@Test
  public void testCreateComparator() throws IOException {
    assertEquals(InnerStoreCellComparator.class,
      createComparator("org.apache.hadoop.hbase.KeyValue$KVComparator").getClass());
    assertEquals(InnerStoreCellComparator.class,
      createComparator(CellComparator.class.getName()).getClass());

    assertEquals(MetaCellComparator.class,
      createComparator("org.apache.hadoop.hbase.KeyValue$MetaComparator").getClass());
    assertEquals(MetaCellComparator.class,
      createComparator("org.apache.hadoop.hbase.CellComparator$MetaCellComparator").getClass());
    assertEquals(MetaCellComparator.class,
      createComparator("org.apache.hadoop.hbase.CellComparatorImpl$MetaCellComparator").getClass());
    assertEquals(MetaCellComparator.class,
      createComparator(MetaCellComparator.META_COMPARATOR.getClass().getName()).getClass());
    assertEquals(MetaCellComparator.META_COMPARATOR.getClass(),
      createComparator(MetaCellComparator.META_COMPARATOR.getClass().getName()).getClass());

    assertEquals(CellComparatorImpl.COMPARATOR.getClass(),
      createComparator(MetaCellComparator.COMPARATOR.getClass().getName()).getClass());

    assertNull(createComparator(Bytes.BYTES_RAWCOMPARATOR.getClass().getName()));
    assertNull(createComparator("org.apache.hadoop.hbase.KeyValue$RawBytesComparator"));

    // Test an invalid comparatorClassName
    assertThrows(IOException.class, () -> createComparator(""));
  }
The number of used fields by version. Indexed by version minus two. Min version that we support
is V2
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestFixedFileTrailer.java