public static RpcClient getClient(String clientName) {
        return CLIENT_MAP.get(clientName);
    }
@Test
    void testGetClient() throws IllegalAccessException {
        // may be null
        assertNull(RpcClientFactory.getClient("notExistClientName"));
        
        clientMapField.set(null, new ConcurrentHashMap<>(Collections.singletonMap("testClient", rpcClient)));
        assertEquals(rpcClient, RpcClientFactory.getClient("testClient"));
    }