code: def testMergeFrom(self):
      message = unittest_pb2.TestAllTypes()
      message.optional_int32 = 1
      message.optional_uint32 = 2
      source = unittest_pb2.TestEmptyMessage()
      source.ParseFromString(message.SerializeToString())
  
      message.ClearField("optional_int32")
      message.optional_int64 = 3
      message.optional_uint32 = 4
      destination = unittest_pb2.TestEmptyMessage()
      destination.ParseFromString(message.SerializeToString())
  
      destination.MergeFrom(source)
      # Check that the fields where correctly merged, even stored in the unknown
      # fields set.
      message.ParseFromString(destination.SerializeToString())
      self.assertEqual(message.optional_int32, 1)
      self.assertEqual(message.optional_uint32, 2)
      self.assertEqual(message.optional_int64, 3)
  
imports: from google.protobuf import unittest_mset_pb2
  from google.protobuf import unittest_pb2
  from google.protobuf import unittest_proto3_arena_pb2
  from google.protobuf.internal import api_implementation
  from google.protobuf.internal import encoder
  from google.protobuf.internal import message_set_extensions_pb2
  from google.protobuf.internal import missing_enum_values_pb2
  from google.protobuf.internal import test_util
  from google.protobuf.internal import testing_refleaks
  from google.protobuf.internal import type_checkers
label_desc: Use image node_id 11 for calling the UnknownFieldsAccessorsTest obj's underlying member method code with example usage: obj.testMergeFrom() without return types