old_contents: import unittest
  import pandas as pd
  import numpy as np
  
  from hidi.factorization import W2VStringTransform
  
  
  class TestW2VStringTransform(unittest.TestCase):
      def setUp(self):
          self.df = pd.DataFrame(np.random.randint(
              0, 50, size=(1000, 2)),
              columns=['item_id', 'link_id'])
          self.w2vstring = W2VStringTransform(get_item_embeddings=False)
          self.string, _ = self.w2vstring.transform(self.df)
  
      def test_w2vstring_returns_string(self):
          self.assertEqual(type("string"), type(self.string))
  
      def test_w2vstring_returns_1000X3_item(self):
          df = self.df
          word_list = self.string.split()
          total_item = 0
          for index in df.index.unique():
              total_item = len(df.loc[index].item_id)*3 + total_item
          self.assertEqual(total_item, len(word_list))
  
new_contents: import unittest
  import pandas as pd
  
  from hidi.factorization import W2VStringTransform
  
  
  class TestW2VStringTransform(unittest.TestCase):
      def setUp(self):
          self.x = ['vevo1', 'vevo2', 'vevo3', 'vevo4',  'vevo5']
          self.y = [1, 1, 1, 2, 3]
          self.df = pd.DataFrame({'link_id': self.y,
                                  'item_id': self.x})
          self.w2vstring = W2VStringTransform()
          self.sentences, _ = self.w2vstring.transform(self.df)
  
      def test_w2vstring_returns_string(self):
          self.assertEqual(type([]), type(self.sentences))
  
      def test_w2vstring_returns_lenX3_item(self):
          length = sum([len(i) for i in self.sentences])
          self.assertEqual(len(set(self.y)), len(self.sentences))
          self.assertEqual(len(self.x)*3, length)
  
subject: modify the w2vstring transfrom testing case