def testMapMessageFieldConstruction(self):
    msg1 = map_unittest_pb2.TestMap()
    msg1.map_string_foreign_message['test'].c = 42
    msg2 = map_unittest_pb2.TestMap(
      map_string_foreign_message=msg1.map_string_foreign_message)
    self.assertEqual(42, msg2.map_string_foreign_message['test'].c)