code: @Test public void appenderRefSettingBySystemProperty() throws JoranException {
    final String propertyName="logback.appenderRef";
    System.setProperty(propertyName,"A");
    configure(ClassicTestConstants.JORAN_INPUT_PREFIX + "appenderRefByProperty.xml");
    final Logger logger=loggerContext.getLogger("ch.qos.logback.classic.joran");
    final ListAppender listAppender=(ListAppender)logger.getAppender("A");
    assertEquals(0,listAppender.list.size());
    final String msg="hello world";
    logger.info(msg);
    assertEquals(1,listAppender.list.size());
    System.clearProperty(propertyName);
  }
  