code: def test_search_bigram(self):
      expected = pd.DataFrame(
          {
              "text": [
                  "Well, speak up man what is it?",
                  "Speak up, speak up, this is a repeat bigram.",
              ],
              "category": ["jay-z/r. kelly", "???"],
              "index": [7, 9],
          }
      ).reset_index(drop=True)
      self.assertIsInstance(self.corpus, CorpusDF)
      returned = self.corpus.search("speak up").reset_index(drop=True)
      pd.testing.assert_frame_equal(
          expected, returned[expected.columns]
      )
  
file_path: scattertext/scattertext/test/test_corpusFromPandas.py
imports: from unittest import TestCase
  import numpy
  import pandas
  from scattertext import chinese_nlp, CorpusDF
  from scattertext import whitespace_nlp
  from scattertext.CorpusFromPandas import CorpusFromPandas
label_desc: Use image node_id 5 for calling the TestCorpusFromPandas obj's underlying member method code with example usage: obj.test_search_bigram() without return types