code: def test_default_servers(app):
      assert app.servers is None
  
      rv = app.test_client().get("/openapi.json")
      assert rv.status_code == 200
      validate_spec(rv.json)
      with app.test_request_context():
          assert rv.json["servers"] == [
              {
                  "url": f"{request.url_root}",
              },
          ]
  
imports: import json
  import pytest
  from flask import request
  from openapi_spec_validator import validate_spec
  from .schemas import Bar
  from .schemas import Baz
  from .schemas import Foo
  from apiflask import APIBlueprint
  from apiflask import Schema
  from apiflask.commands import spec_command
  from apiflask.fields import Integer
label_desc: Use image node_id 11 for calling a global function with example usage: test_default_servers(app) without return types