code: @Test public void testListener() throws Exception {
    ServiceConfig serviceConfig=new ServiceConfig();
    serviceConfig.setListener("mockexporterlistener");
    assertThat(serviceConfig.getListener(),equalTo("mockexporterlistener"));
    Map<String,String> parameters=new HashMap<String,String>();
    parameters.put(Constants.EXPORTER_LISTENER_KEY,"prelistener");
    AbstractServiceConfig.appendParameters(parameters,serviceConfig);
    assertThat(parameters,hasEntry(Constants.EXPORTER_LISTENER_KEY,"prelistener,mockexporterlistener"));
  }
  