new_contents: 
  import unittest
  import numpy as np
  import numpy.testing as test
  from word2gauss.words import Vocabulary, iter_pairs
  
  DTYPE = np.float32
  
  class TestIterPairs(unittest.TestCase):
      def test_iter_pairs(self):
          np.random.seed(1234)
          vocab = Vocabulary({'zero': 0, 'one': 1, 'two': 2})
  
          actual = list(iter_pairs(['zero one two', 'one two zero'],
              vocab, batch_size=2, nsamples=1))
          expected = np.array([[0, 1, 0, 2, 0],
                              [0, 1, 1, 1, 1],
                              [0, 2, 0, 0, 0],
                              [0, 2, 0, 2, 1],
                              [1, 2, 1, 0, 0],
                              [1, 2, 1, 2, 1],
                              [1, 2, 1, 1, 0],
                              [1, 2, 1, 2, 1],
                              [1, 0, 1, 2, 0],
                              [1, 0, 2, 0, 1],
                              [2, 0, 2, 2, 0],
                              [2, 0, 0, 0, 1]], dtype=DTYPE)
          self.assertEqual(len(actual), 1)
          self.assertTrue(np.all(actual[0] == expected))
  
  
  if __name__ == '__main__':
      unittest.main()
  
  
  
subject: Add a test for iter_pairs