code: def test_context_manager(self):
      with vcf_reader.VcfReader.from_file(
          self.sites_vcf, self.options
      ) as f:
          self.assertEqual(
              expected_sites_contigs, list(f.header.contigs)
          )
  
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 14 for calling the WrapVcfReaderTests obj's underlying member method code with example usage: obj.test_context_manager() without return types