class_docstr: Test server
class_docstr_tok: ["Test","server"]
code: def test_bytes_io(self):
      service = api_service.APIService(desc="test")
  
      @service.api(
          path="/echo", input_model=BYTES(), output_model=BYTES()
      )
      def test(b: bytes):
          assert isinstance(b, bytes)
          return b"welcome"
  
      server = HTTPServer(service)
      client = TestClient(server.app)
      response = client.post("/echo", content=b"Hello Towhee")
      self.assertTrue(isinstance(response.content, bytes))
  
file_path: towhee/tests/unittests/serve/http/test_http.py
imports: import unittest
  import typing
  from pydantic import BaseModel
  import numpy
  from towhee.utils.thirdparty.fastapi_utils import fastapi
  from fastapi.testclient import TestClient
  from towhee import api_service, pipe
  from towhee.serve.http.server import HTTPServer
  from towhee.serve.io import JSON, NDARRAY, BYTES
  from towhee.utils.serializer import to_json, from_json
label_desc: Use image node_id 6 for calling the TestHTTPServer obj's underlying member method code with example usage: obj.test_bytes_io() and returns: bytes