code: def test_pickle_unpickle(self):
      ds1 = self._dataset(
          ["utf8_1.txt", "utf8_2.txt"], encoding="utf-8"
      )
      assert ds1[0] == ("テスト1\n", "Test1\n")
      ds2 = pickle.loads(pickle.dumps(ds1))
      assert ds1[1] == ("テスト2\n", "テスト2\n")
      assert ds2[1] == ("テスト2\n", "テスト2\n")
  
imports: from __future__ import unicode_literals
  import os
  import pickle
  import unittest
  import six
  from chainer import datasets
  from chainer import testing
label_desc: Use image node_id 20 for calling the TestTextDataset obj's underlying member method code with example usage: obj.test_pickle_unpickle() without return types