code: public static void constructFakeRaidFile(DistributedFileSystem dfs,
        String filePath, RaidCodec codec) throws IOException {
      long blockSize = 512L;
      byte[] buffer = new byte[(int) (codec.numDataBlocks * blockSize)];
      int[] checksum = new int[codec.numDataBlocks];
      
      OutputStream out = dfs.create(new Path(filePath), true, 1, 
          codec.parityReplication, blockSize);
      random.nextBytes(buffer);
      out.write(buffer);
      out.close();
      
      Path parityTmp = new Path(filePath + "_parity");
      buffer = new byte[(int) (codec.numParityBlocks * blockSize)];
      out = dfs.create(parityTmp, true, 1, 
          codec.parityReplication, blockSize);
      random.nextBytes(buffer);
      out.write(buffer);
      out.close();
      
      FileStatus stat = dfs.getFileStatus(new Path(filePath));
      dfs.setTimes(parityTmp, stat.getModificationTime(), stat.getAccessTime());
      
      dfs.merge(parityTmp, new Path(filePath), codec.id, checksum);
      
    }
docs: This function create two mock source and parity files and merge them.