Can't test engine routes under Rails 3.2 + Rspec 2.13 - ruby-on-rails-3

Question

In my engine 'Utilizer', I'm trying to test routes with Rspec 3.2.
Namespace are isolated
# lib/utilizer/engine.rb
module Utilizer
class Engine < ::Rails::Engine
isolate_namespace Utilizer
...
end
end
The engine is mounted to the dummy app:
# spec/dummy/config/routes.rb
Rails.application.routes.draw do
mount Utilizer::Engine => "/utilizer", as: 'utilizer'
end
To the spec_helper.rb I've added a couple of configures as below (from here):
# spec/spec_helper.rb
RSpec.configure do |config|
...
config.before(:each, type: :routing) { #routes = Utilizer::Engine.routes }
...
end
When I defined a route:
# config/routes.rb
Utilizer::Engine.routes.draw do
resources :auths, id: /\d+/, only: [:destroy]
end
Rake shows it properly for the dummy app:
$ spec/dummy > bundle exec rake routes
$ utilizer /utilizer Utilizer::Engine
$ Routes for Utilizer::Engine:
$ auth DELETE /auths/:id(.:format) utilizer/auths#destroy {:id=>/\d+/}
BUT both Rspec tests
# spec/routing/auths_routing_spec.rb
require 'spec_helper'
describe "Auths page routing" do
let!(:auth) { create(:utilizer_auth) } # factory is working properly by itself
describe "#destroy" do
let!(:action) { { controller: "utilizer/auths", action: "destroy", id: auth.id } }
specify { { delete: "/auths/#{ auth.id }" }.should route_to(action) }
specify { { delete: auth_path(auth) }.should route_to(action) }
end
end
fail with errors (for the first and second tests correspondingly):
No route matches "/auths/1"
No route matches "/utilizer/auths/1"
But, Holmes, why?

Answer 1

Since RSpec 2.14 you can use the following:
describe "Auths page routing" do
routes { Utilizer::Engine.routes }
# ...
end
Source: https://github.com/rspec/rspec-rails/pull/668

Answer 2

I've fount a solution in Exoth's comment at the end of this discussion on Github (thanks to Brandan).
In my spec_helper instead of
config.before(:each, type: :routing) { #routes = Utilizer::Engine.routes }
I use
config.before(:each, type: :routing) do
#routes = Utilizer::Engine.routes
assertion_instance.instance_variable_set(:#routes, Utilizer::Engine.routes)
end
and it works.