code: def test_build_vaf_histograms(self):
      chart = vcf_stats_vis._build_vaf_histograms(
          VIS_DATA["vaf_histograms_by_genotype"]
      )
      self.assertTrue(is_an_altair_chart(chart[0]))
      self.assertTrue(is_an_altair_chart(chart[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 10 for calling the VcfStatsVisTest obj's underlying member method code with example usage: obj.test_build_vaf_histograms() without return types