code: import pandas
  
  from ds_utils.strings import append_tags_to_frame, extract_significant_terms_from_subset
  
  
  def test_append_tags_to_frame():
      x_train = pandas.DataFrame([{"article_name": "1", "article_tags": "ds,ml,dl"},
                                  {"article_name": "2", "article_tags": "ds,ml"}])
      x_test = pandas.DataFrame([{"article_name": "3", "article_tags": "ds,ml,py"}])
  
      x_train_expected = pandas.DataFrame([{"article_name": "1", "tag_ds": 1, "tag_ml": 1, "tag_dl": 1},
                                           {"article_name": "2", "tag_ds": 1, "tag_ml": 1, "tag_dl": 0}],
                                          columns=["article_name", "tag_dl", "tag_ds", "tag_ml"])
      x_test_expected = pandas.DataFrame([{"article_name": "3", "tag_ds": 1, "tag_ml": 1, "tag_dl": 0}],
                                         columns=["article_name", "tag_dl", "tag_ds", "tag_ml"])
  
      x_train_with_tags, x_test_with_tags = append_tags_to_frame(x_train, x_test, "article_tags", "tag_")
      pandas.testing.assert_frame_equal(x_train_expected, x_train_with_tags, check_like=True)
      pandas.testing.assert_frame_equal(x_test_expected, x_test_with_tags, check_like=True)
  
  
  def test_significant_terms():
      corpus = ['This is the first document.', 'This document is the second document.', 'And this is the third one.',
                'Is this the first document?']
      data_frame = pandas.DataFrame(corpus, columns=["content"])
      subset_data_frame = data_frame[data_frame.index > 1]
      terms = extract_significant_terms_from_subset(data_frame, subset_data_frame, "content")
  
      expected = pandas.Series(
          [1.0, 1.0, 1.0, 0.6666666666666666, 0.6666666666666666, 0.6666666666666666, 0.5, 0.25, 0.0],
          index=['third', 'one', 'and', 'this', 'the', 'is', 'first', 'document', 'second'])
  
      pandas.testing.assert_series_equal(expected, terms)
  
apis: pandas.Series pandas.testing.assert_series_equal pandas.DataFrame pandas.testing.assert_frame_equal