class_docstr: Tests for VcfWriter.
code: def write_variant_to_tempfile(self, variant):
      output_path = test_utils.test_tmpfile("test.vcf")
      header = variants_pb2.VcfHeader(
          contigs=[reference_pb2.ContigInfo(name="20")],
          sample_names=[call.call_set_name for call in variant.calls],
          formats=[
              variants_pb2.VcfFormatInfo(
                  id="DP",
                  number="1",
                  type="Integer",
                  description="Read depth",
              ),
              variants_pb2.VcfFormatInfo(
                  id="AD",
                  number="R",
                  type="Integer",
                  description="Read depth for each allele",
              ),
          ],
      )
      writer = vcf.VcfWriter(output_path, header=header)
      with writer:
          writer.write(variant)
      return output_path
  
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 2 for calling the VcfWriterTests obj's underlying member method code with example usage: obj.write_variant_to_tempfile(variant) and returns: output_path