Rails Rspec test session variable in decorator - ruby-on-rails

Question

I have a decorator that receives the application controller as a variable in order to access session variables. Something like:
navigation = NavigationDecorator(user_id, self)
Self being the ApplicationController.
Everything works fine, but now I have to test it and in Rspec I did
navigation = NavigationDecorator(user_id, ApplicationController.new)
During my tests I get:
ActionController::Metal#session delegated to #_request.session, but #_request is nil: #<ApplicationController:0x000000161363f0 #_routes=nil, #_action_has_layout=true, #_headers={"Content-Type"=>"text/html"}, #_status=200, #_request=nil, #_response=nil>
Updating:
I use it like this:
def initialize(user, controller)
#controller = controller
...
end
def retrieve_user_id
user_id = #controller.session[:temporary_id] if #controller.session[:temporary_id]
super
end

Answer 1

I'd propose to stub controller in the test, because since you're writing unit test (you're writing unit test, right?) you want to isolate your system under test (NavigationDecorator) from its dependencies (controller). You can write this test:
describe NavigationDecorator do
context 'user_id'
it 'should take id from session' do
session = { temporary_id: 'temporary' }
controller = instance_double('ApplicationController', session: session)
user = instance_double('User', id: 'user_id')
subject = described_class.new(user, session)
expect(subject.retrieve_user_id).to eq session[:temporary_id]
end
end
end
The test shows us that we have unneeded dependency (controller) and it would be cleaner to pass session right away (if you can, of course):
describe NavigationDecorator do
context 'user_id'
it 'should take id from session' do
session = { temporary_id: 'temporary' }
subject = described_class.new('local id', session)
expect(subject.retrieve_user_id).to eq session[:temporary_id]
end
it 'should take id from user when session is empty' do
controller = instance_double('ApplicationController', session: {})
user = instance_double('User', id: 'user_id')
subject = described_class.new(user, session)
expect(subject.retrieve_user_id).to eq user.id
end
end
end