public static ExtensionMappingInstructionWrapper extension(ExtensionTreatment extension,
                                                               DeviceId deviceId) {
        checkNotNull(extension, "Extension instruction cannot be null");
        checkNotNull(deviceId, "Device ID cannot be null");
        return new ExtensionMappingInstructionWrapper(extension, deviceId);
    }
@Test
    public void testExtensionMethod() {
        final MappingInstruction instruction =
                MappingInstructions.extension(extensionTreatment1, deviceId1);
        final MappingInstructions.ExtensionMappingInstructionWrapper wrapper =
                checkAndConvert(instruction,
                                MappingInstruction.Type.EXTENSION,
                                MappingInstructions.ExtensionMappingInstructionWrapper.class);
        assertThat(wrapper.deviceId(), is(deviceId1));
        assertThat(wrapper.extensionMappingInstruction(), is(extensionTreatment1));
    }