code: def test_state(self):
      def predict(input, history):
          if history is None:
              history = ""
          history += input
          return history, history
  
      io = Interface(
          predict, ["textbox", "state"], ["textbox", "state"]
      )
      app, _, _ = io.launch(prevent_thread_lock=True)
      client = TestClient(app)
      response = client.post(
          "/api/predict/",
          json={
              "data": ["test", None],
              "fn_index": 0,
              "session_hash": "_",
          },
      )
      output = dict(response.json())
      assert output["data"] == ["test", None]
      response = client.post(
          "/api/predict/",
          json={
              "data": ["test", None],
              "fn_index": 0,
              "session_hash": "_",
          },
      )
      output = dict(response.json())
      assert output["data"] == ["testtest", None]
  
imports: import functools
  import os
  import tempfile
  from contextlib import asynccontextmanager, closing
  from unittest import mock
  import gradio_client
  import numpy
  import pandas
  import pytest
  import starlette.routing
  from fastapi import FastAPI
  from fastapi.testclient import TestClient
  from gradio_client import media_data
  import gradio
  from gradio import Blocks, Button, Interface, Number, Textbox, close_all, routes, wasm_utils
  from gradio.route_utils import FnIndexInferError
label_desc: Use image node_id 13 for calling the TestRoutes obj's underlying member method code with example usage: obj.test_state() and returns: history,  history