public void addAppender(Appender<E> newAppender) {
    if (newAppender == null) {
      throw new IllegalArgumentException("Null argument disallowed");
    }
     appenderList.addIfAbsent(newAppender);
  }
@Test
  public void testAddAppender() throws Exception {
    TestEvent event = new TestEvent();
    NOPAppender<TestEvent> ta = new NOPAppender<TestEvent>();
    ta.start();
    aai.addAppender(ta);
    ta = new NOPAppender<TestEvent>();
    ta.setName("test");
    ta.start();
    aai.addAppender(ta);
    int size = aai.appendLoopOnAppenders(event);
    assertTrue("Incorrect number of appenders", size == 2);
  }