code: def test_vcf_samples(self):
      self.assertEqual(list(self.sites_reader.header.sample_names), [])
      self.assertEqual(
          list(self.samples_reader.header.sample_names),
          ["NA12878_18_99"],
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from absl.testing import absltest
  from third_party.nucleus.io.python import vcf_reader
  from third_party.nucleus.protos import reference_pb2
  from third_party.nucleus.protos import variants_pb2
  from third_party.nucleus.testing import test_utils
  from third_party.nucleus.util import ranges
label_desc: Use image node_id 6 for calling the WrapVcfReaderTests obj's underlying member method code with example usage: obj.test_vcf_samples() without return types