Undefined method `signed' for #<Rack::Test::CookieJar>

Hello,

In my integration test, I want to simulate the user cookie is set. I
store
an authentication token as a stored cookie.
So in my test. I write:

cookies.signed[:authentication_token] = user.authentication_token

Unforunately, it sends me a Undefined method `signed’ for
#Rack::Test::CookieJar error.
What should I do?