@Test
public void testRecover() throws TException, InterruptedException {

    ServerSelector serverSelector = new ServerSelector(
            "appId", Arrays.asList(NO_AVAILABLE_INSTANCE_1, NO_AVAILABLE_INSTANCE_2), "dasClientVersion", "ppdaiClientVersion", "clientAddress"
    );
    try {
         serverSelector.execute(REQUEST);
         fail();
    } catch (Exception e){
        //expected
    }
    serverSelector.serverInstances.add(AVAILABLE_INSTANCE_1);
    TimeUnit.SECONDS.sleep(ServerSelector.checkInterval + 1);//Wait for heart beat get correct instance
    DasResult response = serverSelector.execute(REQUEST);
    Assert.assertNotNull(response);
}