code: def test_flow_incompatibility_with_singleton(protocols):
      class First(Executor):
          @requests
          def foo(
              self, docs: DocList[TextDoc], **kwargs
          ) -> DocList[TextDoc]:
              pass
  
      class Second(Executor):
          @requests
          def foo(self, doc: ImageDoc, **kwargs) -> ImageDoc:
              pass
  
      f = Flow(protocol=protocols).add(uses=First).add(uses=Second)
  
      with pytest.raises(RuntimeFailToStart):
          with f:
              pass
  
file_path: jina/tests/integration/docarray_v2/test_singleton.py
imports: import pytest
  from jina import Flow, Executor, Deployment, requests, Client
  from docarray import BaseDoc, DocList
  from docarray.documents import TextDoc, ImageDoc
  from jina.helper import random_port
  from jina.excepts import RuntimeFailToStart
  import asyncio
label_desc: Use image node_id 5 for calling a global function with example usage: test_flow_incompatibility_with_singleton(protocols) without return types