class_docstr: Test the functionality of the VcfHeaderCache class.
code: def setUp(self):
      self.vcf_reader = vcf.VcfReader(
          test_utils.genomics_core_testdata("test_sites.vcf")
      )
      self.cache = self.vcf_reader.field_access_cache
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from absl.testing import absltest
  from absl.testing import parameterized
  from etils import epath
  from third_party.nucleus.io import vcf
  from third_party.nucleus.protos import reference_pb2
  from third_party.nucleus.protos import struct_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 1 for calling the VcfHeaderCacheTests obj's underlying member method code with example usage: obj.setUp() without return types