code: def testSerializeProto3(self):
      # Verify that proto3 doesn't preserve unknown fields.
      message = unittest_proto3_arena_pb2.TestEmptyMessage()
      message.ParseFromString(self.all_fields_data)
      self.assertEqual(0, len(message.SerializeToString()))
  
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 3 for calling the UnknownFieldsTest obj's underlying member method code with example usage: obj.testSerializeProto3() without return types