code: def test_include_mathjax_cdn_html(self):
      html = self._read_html(
          plotly.offline.plot(
              fig,
              include_mathjax="cdn",
              output_type="file",
              filename=html_filename,
              auto_open=False,
          )
      )
  
      self.assertIn(plotly_config_script, html)
      self.assertIn(PLOTLYJS, html)
      self.assertIn(mathjax_cdn_script, html)
      self.assertIn(mathjax_font, html)
  
imports: import json
  import os
  from unittest import TestCase
  import pytest
  import plotly
  import plotly.io
  from plotly.io._utils import plotly_cdn_url
label_desc: Use image node_id 21 for calling the PlotlyOfflineTestCase obj's underlying member method code with example usage: obj.test_include_mathjax_cdn_html() without return types