code: @Test(expected=RpcException.class) public void testFail() throws Exception {
    URL url=URL.valueOf("test://test");
    url=url.addParameter(Constants.INTERFACE_KEY,"org.apache.dubbo.rpc.file.TpsService");
    url=url.addParameter(Constants.TPS_LIMIT_RATE_KEY,5);
    Invoker<TpsLimitFilterTest> invoker=new MyInvoker<TpsLimitFilterTest>(url);
    Invocation invocation=new MockInvocation();
    for (int i=0; i < 10; i++) {
      try {
        filter.invoke(invoker,invocation);
      }
   catch (    Exception e) {
        assertTrue(i >= 5);
        throw e;
      }
    }
  }
  