fromflaskimportFlask,redirect,url_forfromflask.testingimportFlaskClientapp=Flask(__name__)classCustomClient(FlaskClient):defopen(self,*args,**kwargs):kwargs["headers"]= {"Extra-Key":"extra value"}returnsuper().open(*args,**kwargs)@app.route("/")defhome():returnredirect(url_for("test"))@app.route("/test")deftest():return"Hello, World!"app.test_client_class=CustomClientc=app.test_client()rv=c.get("/",follow_redirects=True)print(rv.data)

Traceback (most recent call last):  File"/home/david/Projects/flask/example.py", line21, in<module>    rv= c.get("/",follow_redirects=True)  File"/home/david/.virtualenvs/flask/lib/python3.8/site-packages/werkzeug/test.py", line1029, ingetreturnself.open(*args,**kw)  File"/home/david/Projects/flask/example.py", line9, inopenreturnsuper().open(*args,**kwargs)  File"/home/david/Projects/flask/src/flask/testing.py", line222, inopenreturn Client.open(  File"/home/david/.virtualenvs/flask/lib/python3.8/site-packages/werkzeug/test.py", line1016, inopen    environ, response=self.resolve_redirect(  File"/home/david/.virtualenvs/flask/lib/python3.8/site-packages/werkzeug/test.py", line948, inresolve_redirectreturnself.open(builder,as_tuple=True,buffered=buffered)  File"/home/david/Projects/flask/example.py", line9, inopenreturnsuper().open(*args,**kwargs)  File"/home/david/Projects/flask/src/flask/testing.py", line215, inopen    builder= EnvironBuilder(self.application,*args,**kwargs)  File"/home/david/Projects/flask/src/flask/testing.py", line73, in__init__    url= url_parse(path)  File"/home/david/.virtualenvs/flask/lib/python3.8/site-packages/werkzeug/urls.py", line457, inurl_parse    i= url.find(s(":"))AttributeError:'EnvironBuilder' object has no attribute 'find'