@Override
    protected void initializeTable(Connection connection, TableName tableName) throws IOException {
      super.initializeTable(connection, tableName);
      ConnectionForMergeTesting cft = (ConnectionForMergeTesting) connection;
      sizeCalculator = cft.getRegionSizeCalculator();
    }
Exclude regions which contain rows starting with "b".
hbase-mapreduce/src/test/java/org/apache/hadoop/hbase/mapreduce/TestTableInputFormatBase.java