code: def test_flatten_not_nested(self):
      not_nested = [1, 2, 3, 4, 5, 6]
      expected = [1, 2, 3, 4, 5, 6]
      self.assertEqual(utils.flatten(not_nested), expected)
  
imports: import logging
  import unittest
  import numpy
  from gensim import utils
  from gensim.test.utils import datapath, get_tmpfile
label_desc: Use image node_id 11 for calling the TestWindowing obj's underlying member method code with example usage: obj.test_flatten_not_nested() without return types