So, this is an interesting question. Yes, you should definitely (IMO) test authentication separately from the target method/action. Each of these constitutes a unit of functionality and should be tested as such.
In my current project, I'm favoring POROs (I often keep them in a directory called 'managers' although I know many people prefer to call them 'services') for all sorts of things because it lets me isolate functionality and test it independently. So, I might end up with something like:
# controllers/foo_controller.rb
class FooController < ApplicationController
before_action :authenticate
def create
@results = FooManager.create(params)
redirect_to (@results[:success] ? my_happy_path : my_sad_path)
end
def authenticate
redirect_to unauthorized_path unless AuthenticationManager.authenticate(params, request)
end
end
# managers/foo_manager.rb
class FooManager
class << self
def create(params)
# do a bunch of great stuff and return a hash (perhaps a
# HashWithIndifferentAccess, if you like) which will
# allow for evaluation of @results[:success] back in the
# controller.
end
end
end
# managers/authentication_manager.rb
class AuthenticationManager
class << self
def authenticate(params, request)
# do a bunch of great stuff and return a boolean
end
end
end
With an approach like this, I can very easily test FooManager.create
and AuthenticationManager.authenticate
(as well as FooController.create
and FooController.authenticate
routing) all independently. Hooray!
Now, whether your authentication framework or controller method is behaving correctly at a unit level, as Dave points out very well, is a separate issue from whether your entire system is behaving as expected. I'm with him on having high-level integration tests so you're clear about what 'done' looks like and you know when to holler 'ship it!'