code: def test_close(self):
      ds = self._dataset("ascii_1.txt")
      assert ds[0] == "hello\n"
      ds.close()
      with self.assertRaises(ValueError):
          ds[0]
  
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 3 for calling the TestTextDataset obj's underlying member method code with example usage: obj.test_close() without return types