code: def test_altair_chart_to_html(self):
      df = pd.DataFrame({"x": ["A", "B"], "y": [28, 55]})
      c = alt.Chart(df).mark_bar().encode(x="x", y="y")
      html_string = vcf_stats_vis._altair_chart_to_html(
          altair_chart=c, download_filename="TEST_DOWNLOAD_FILENAME"
      )
      import_base = (
          'src="https://storage.googleapis.com/deepvariant/lib/vega/'
      )
      self.assertNotEqual(
          html_string.find(
              import_base + 'vega@%s"' % (vcf_stats_vis.VEGA_VERSION,)
          ),
          -1,
      )
      self.assertNotEqual(
          html_string.find(
              import_base
              + 'vega-lite@%s"' % (vcf_stats_vis.VEGA_LITE_VERSION,)
          ),
          -1,
      )
      self.assertNotEqual(
          html_string.find(
              import_base
              + 'vega-embed@%s"' % (vcf_stats_vis.VEGA_EMBED_VERSION,)
          ),
          -1,
      )
      self.assertEqual(html_string.find("jsdelivr.net"), -1)
      self.assertNotEqual(
          html_string.find("TEST_DOWNLOAD_FILENAME"), -1
      )
  
imports: import os
  import tempfile
  from absl.testing import absltest
  import altair
  import pandas
  import tensorflow
  from deepvariant import vcf_stats_vis
label_desc: Use image node_id 14 for calling the VcfStatsVisTest obj's underlying member method code with example usage: obj.test_altair_chart_to_html() without return types