code: def test_blueprint_url_processors(app, client):
      bp = flask.Blueprint(
          "frontend", __name__, url_prefix="/<lang_code>"
      )
  
      @bp.url_defaults
      def add_language_code(endpoint, values):
          values.setdefault("lang_code", flask.g.lang_code)
  
      @bp.url_value_preprocessor
      def pull_lang_code(endpoint, values):
          flask.g.lang_code = values.pop("lang_code")
  
      @bp.route("/")
      def index():
          return flask.url_for(".about")
  
      @bp.route("/about")
      def about():
          return flask.url_for(".index")
  
      app.register_blueprint(bp)
  
      assert client.get("/de/").data == b"/de/about"
      assert client.get("/de/about").data == b"/de/"
  
imports: import pytest
  from jinja2 import TemplateNotFound
  from werkzeug.http import parse_cache_control_header
  import flask
label_desc: Use image node_id 6 for calling a global function with example usage: test_blueprint_url_processors(app, client) and returns: flask, flask