def setUpClass(cls):
    # At the moment, reference cycles between DescriptorPool and Message classes
    # are not detected and these objects are never freed.
    # To avoid errors with ReferenceLeakChecker, we create the class only once.
    file_desc = """
      name: "f/f.msg2"
      package: "f"
      message_type {
        name: "msg1"
        field {
          name: "payload"
          number: 1
          label: LABEL_OPTIONAL
          type: TYPE_STRING
        }
      }
      message_type {
        name: "msg2"
        field {
          name: "field"
          number: 1
          label: LABEL_OPTIONAL
          type: TYPE_MESSAGE
          type_name: "msg1"
        }
      }
    """
    pool = descriptor_pool.DescriptorPool()
    desc = descriptor_pb2.FileDescriptorProto()
    text_format.Parse(file_desc, desc)
    pool.Add(desc)
    cls.proto_cls = message_factory.MessageFactory(pool).GetPrototype(
        pool.FindMessageTypeByName('f.msg2'))