code: def test_filter(self):
      def _filter(line):
          return line != "world\n"
  
      ds = self._dataset(["ascii_1.txt"], filter_func=_filter)
      assert len(ds) == 2
      assert ds[0] == "hello\n"
      assert ds[1] == "test\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 18 for calling the TestTextDataset obj's underlying member method code with example usage: obj.test_filter() and returns: unknown