code: @Test public void testSyncCallback(){
    @SuppressWarnings("unchecked") Invoker<DemoService> invoker=mock(Invoker.class);
    given(invoker.isAvailable()).willReturn(true);
    given(invoker.getInterface()).willReturn(DemoService.class);
    RpcResult result=new RpcResult();
    result.setValue("High");
    given(invoker.invoke(invocation)).willReturn(result);
    URL url=URL.valueOf("test://test:11/test?group=dubbo&version=1.1");
    given(invoker.getUrl()).willReturn(url);
    Result filterResult=eventFilter.invoke(invoker,invocation);
    assertEquals("High",filterResult.getValue());
  }
  