code: def test_vcf_header(self):
      header = self.sites_reader.header
      expected1 = variants_pb2.VcfStructuredExtra(
          key="ALT",
          fields=[
              variants_pb2.VcfExtra(key="ID", value="NON_REF"),
              variants_pb2.VcfExtra(
                  key="Description",
                  value="Represents	any	possible	alternative	allele	at	th"
                  "is	location",
              ),
          ],
      )
      expected2 = variants_pb2.VcfStructuredExtra(
          key="META",
          fields=[
              variants_pb2.VcfExtra(key="ID", value="TESTMETA"),
              variants_pb2.VcfExtra(key="Description", value="blah"),
          ],
      )
      self.assertLen(header.structured_extras, 2)
      self.assertEqual(header.structured_extras[1], expected2)
      self.assertEqual(header.structured_extras[0], expected1)
  
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 3 for calling the WrapVcfReaderTests obj's underlying member method code with example usage: obj.test_vcf_header() without return types