gistfile1.rb

@alt = ActionDispatch::Routing::RouteSet.new

@alt.draw do
  controller :custom do
    resources :tweets
  end
end

def app
  @alt
end

include Rack::Test::Methods
get '/tweets'

# => ActionController::RoutingError: uninitialized constant TweetsController

include @alt.url_helpers

hash_for_tweets_path

# => {:controller=>"tweets", :action=>"create", :use_route=>"tweets", :only_path=>true}