public OpenConfigTransceiverHandler addConfig(OpenConfigConfigOfTransceiverHandler config) {
        modelObject.config(config.getModelObject());
        return this;
    }
@Test
    public void testAddConfig() {
        // test Handler
        OpenConfigTransceiverHandler transceiver = new OpenConfigTransceiverHandler(parent);

        // call addConfig
        OpenConfigConfigOfTransceiverHandler config = new OpenConfigConfigOfTransceiverHandler(transceiver);

        // expected ModelObject
        DefaultTransceiver modelObject = new DefaultTransceiver();
        DefaultConfig con = new DefaultConfig();
        modelObject.config(con);

        assertEquals("[NG]addConfig:ModelObject(Config added) is not an expected one.\n",
                     modelObject, transceiver.getModelObject());
    }