code: def test_count_titv(self):
      variant_stats_lite = collections.namedtuple(
          "variant_stats_lite", ["is_transition", "is_transversion"]
      )
      variant_stats = [
          variant_stats_lite(is_transition=True, is_transversion=False),
          variant_stats_lite(is_transition=True, is_transversion=False),
          variant_stats_lite(is_transition=True, is_transversion=False),
          variant_stats_lite(is_transition=False, is_transversion=True),
          variant_stats_lite(is_transition=False, is_transversion=True),
          variant_stats_lite(
              is_transition=False, is_transversion=False
          ),
      ]
      truth_counts = {"Transition": 3, "Transversion": 2}
      self.assertEqual(
          vcf_stats._count_titv(variant_stats), truth_counts
      )
  
imports: import collections
  import json
  import os
  import tempfile
  from absl.testing import absltest
  from absl.testing import parameterized
  import tensorflow
  from deepvariant import testdata
  from deepvariant import vcf_stats
  from third_party.nucleus.io import vcf
  from third_party.nucleus.testing import test_utils
  from third_party.nucleus.util import variant_utils
  from third_party.nucleus.util import variantcall_utils
label_desc: Use image node_id 7 for calling the VcfStatsTest obj's underlying member method code with example usage: obj.test_count_titv() without return types