code: def test_set_format(self, field_name, value, reader, expected):
      if reader is not None:
          reader = mock.Mock()
          reader.field_access_cache.format_field_set_fn.return_value = (
              struct_utils.set_string_field
          )
      call = variants_pb2.VariantCall()
      variantcall_utils.set_format(call, field_name, value, reader)
      actual = call.info[field_name].values
      self._assert_struct_lists_equal(actual, expected)
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import functools
  from absl.testing import absltest
  from absl.testing import parameterized
  import mock
  from third_party.nucleus.protos import struct_pb2
  from third_party.nucleus.protos import variants_pb2
  from third_party.nucleus.util import struct_utils
  from third_party.nucleus.util import variantcall_utils
label_desc: Use image node_id 2 for calling the VariantcallUtilsTests obj's underlying member method code with example usage: obj.test_set_format(field_name, value, reader, expected) without return types