Sign in and sign out problem in Rails

Question

I am programming a simple app to manage users in Ruby on Rails.I read RoR Tutorial from http://ruby.railstutorial.org/chapters/sign-in-sign-out#top to sign in and sign out my app. I implemented the same configuration as it said:

_sessions_helper.rb_def sign_out  self.current_user = nil cookies.delete(:remember_token)end    
_sessions_controller.rb_ def destroy sign_out redirect_to root_url end
_application.html.erb_
_routes.rb_ match '/signout', to: 'sessions#destroy', via: 'delete'

I am able to sign in, but I can't sign out. The problem is that there are not any log error and I don't know what to do.