docstr: Router can't accept a route with no variables used in the output field
docstr_tok: ["Router","ca","n't","accept","a","route","with","no","variables","used","in","the","output","field"]
code: def test_no_vars_in_output_route_but_with_output_name(self):
      """
      Router can't accept a route with no variables used in the output field
      """
      routes = [
          {
              "condition": "{{streams|length > 2}}",
              "output": "This is a constant",
              "output_name": "enough_streams",
              "output_type": str,
          }
      ]
      router = ConditionalRouter(routes)
      kwargs = {"streams": [1, 2, 3], "query": "Haystack"}
      result = router.run(**kwargs)
      assert result == {"enough_streams": "This is a constant"}
  
imports: import copy
  from typing import List
  from unittest import mock
  import pytest
  from haystack.components.routers import ConditionalRouter
  from haystack.components.routers.conditional_router import NoRouteSelectedException
  from haystack.dataclasses import ChatMessage
label_desc: Use image node_id 5 for calling the TestRouter obj's underlying member method code with example usage: obj.test_no_vars_in_output_route_but_with_output_name() without return types