code: def test_len(self):
      ds = self._dataset("ascii_1.txt")
      assert len(ds) == 3
  
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 5 for calling the TestTextDataset obj's underlying member method code with example usage: obj.test_len() without return types