class_docstr: Tests for VcfWriter.
code: def test_single_value_format_field(self, variant, expected_vcf_line):
      self.assertWrittenVCFRecordsEqual(
          self.write_variant_to_tempfile(variant), [expected_vcf_line]
      )
  
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 3 for calling the VcfWriterTests obj's underlying member method code with example usage: obj.test_single_value_format_field(variant, expected_vcf_line) without return types