code: def test_chart_type_negative_control(self):
      self.assertFalse(is_an_altair_chart("some string"))
      self.assertFalse(is_an_altair_chart(None))
  
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 4 for calling the VcfStatsVisTest obj's underlying member method code with example usage: obj.test_chart_type_negative_control() without return types