code: def test_calculate_length_statistics(
      sources, targets, expected_num_sents, expected_mean, expected_std
  ):
      length_statistics = data_io.calculate_length_statistics(
          sources, targets, 5, 5
      )
      assert len(sources[0]) == len(targets[0])
      assert length_statistics.num_sents == expected_num_sents
      assert np.isclose(
          length_statistics.length_ratio_mean, expected_mean
      )
      assert np.isclose(
          length_statistics.length_ratio_std, expected_std
      )
  
imports: import os
  import random
  from tempfile import TemporaryDirectory
  from typing import Optional, List, Tuple
  import numpy
  import pytest
  import torch
  from sockeye import constants
  from sockeye import data_io
  from sockeye import utils
  from sockeye import vocab
  from sockeye.test_utils import tmp_digits_dataset
  from sockeye.utils import SockeyeError, get_tokens, seed_rngs
label_desc: Use image node_id 21 for calling a global function with example usage: test_calculate_length_statistics(sources, targets, expected_num_sents, expected_mean, expected_std) without return types