private void verifyCornerHoles(CatalogJanitor janitor, TableName tableName) throws IOException {
    RegionStateStore regionStateStore =
      TEST_UTIL.getHBaseCluster().getMaster().getAssignmentManager().getRegionStateStore();
    RegionInfo firstRegion = getRegionInfo(tableName, "".getBytes());
    RegionInfo secondRegion = getRegionInfo(tableName, "bbb".getBytes());
    regionStateStore.deleteRegion(firstRegion);
    LinkedList<Pair<RegionInfo, RegionInfo>> holes = getHoles(janitor, tableName);

    assertEquals(1, holes.size());
    Pair<RegionInfo, RegionInfo> regionInfoRegionInfoPair = holes.get(0);
    assertTrue(regionInfoRegionInfoPair.getFirst().getTable()
      .equals(RegionInfoBuilder.UNDEFINED.getTable()));
    assertTrue(regionInfoRegionInfoPair.getSecond().getTable().equals(tableName));
    assertTrue(
      regionInfoRegionInfoPair.getSecond().getEncodedName().equals(secondRegion.getEncodedName()));

    RegionInfo lastRegion = getRegionInfo(tableName, "zzz".getBytes());
    RegionInfo secondLastRegion = getRegionInfo(tableName, "yyy".getBytes());
    regionStateStore.deleteRegion(lastRegion);
    holes = getHoles(janitor, tableName);
    assertEquals(2, holes.size());
    regionInfoRegionInfoPair = holes.get(1);
    assertTrue(regionInfoRegionInfoPair.getFirst().getEncodedName()
      .equals(secondLastRegion.getEncodedName()));
    assertTrue(regionInfoRegionInfoPair.getSecond().getTable()
      .equals(RegionInfoBuilder.UNDEFINED.getTable()));
  }
Take last byte and add one to it.
hbase-server/src/test/java/org/apache/hadoop/hbase/master/janitor/TestCatalogJanitorCluster.java