code: def test_transform_unknown_token(self):
      it = IndexTransformer()
      it.fit(self.x, self.y)
  
      x_train, y_train = [["aaa"]], [["X"]]
      X, y = it.transform(x_train, y_train)
      words, chars = X
  
      # Check sequence length.
      self.assertEqual(len(words), len(x_train))
      self.assertEqual(len(chars), len(x_train))
      self.assertEqual(len(y), len(y_train))
  
      # Check sequence type.
      self.assertIsInstance(words, np.ndarray)
      self.assertIsInstance(chars, np.ndarray)
      self.assertIsInstance(y, np.ndarray)
  
imports: import os
  import shutil
  import unittest
  import numpy
  from anago.preprocessing import IndexTransformer, pad_nested_sequences
label_desc: Use image node_id 9 for calling the TestIndexTransformer obj's underlying member method code with example usage: obj.test_transform_unknown_token() without return types