code: def df():
      mock_text = {
          "cord_uid": ["ej795nks", "9mzs5dl4", "u7lz3spe"],
          "doi": [
              "10.1289/ehp.7117",
              "10.1289/ehp.7491",
              "10.1371/journal.pmed.0030149",
          ],
          "title": [
              "Understanding the Spatial Clustering of",
              "The Application of the Haddon Matrix to",
              "Cynomolgus Macaque as an Animal Model for",
          ],
          "authors": [
              "Lai, P.C.; Wong, C.M.; Hedley, A.J.; Lo,",
              "Barnett, Daniel J.; Balicer, Ran D.;",
              "Lawler, James V; Endy, Timothy P; Hensley,",
          ],
          "journal": [
              "Environ Health Perspect",
              "Environ Health Perspect",
              "PLoS Med",
          ],
          "abstract": [
              "We applied cartographic and geostatistical met",
              "State and local health departments continue to",
              "BACKGROUND: The emergence of severe acute resp.",
          ],
          "publish_time": ["2004-07-27", "2005-02-02", "2006-04-18"],
          "url": [
              "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11",
              "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12",
              "https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13",
          ],
          "full_text": [
              "Since the emergence and rapid spread of the e...",
              "sudden fever and dry cough, along with chills",
              "The emergence of severe acute respiratory syndrome (SARS)",
          ],
      }
      return pd.DataFrame(mock_text)
  
file_path: recommenders/tests/unit/recommenders/models/test_tfidf_utils.py
imports: import pytest
  import scipy
  import pandas
  from recommenders.models.tfidf.tfidf_utils import TfidfRecommender
label_desc: Use image node_id 1 for calling a global function with example usage: df() and returns: pd