base_controller.rb

class Admin::BaseController < ApplicationController
	before_filter :require_admin
	
	protected
	
	def require_admin
		redirect_to error_path(403) unless current_user.is_administrator?
	end
end

base_controller_spec.rb

require 'spec_helper'

describe Admin::BaseController do
	should_be_an_instance_of Admin::BaseController
	should_descend_from ApplicationController

	context 'before_filter' do
		it 'should respond to :require_admin' do
			controller.should respond_to(:require_admin)
		end
	end
end

home_controller_spec.rb

describe Admin::HomeController do
	should_be_an_instance_of Admin::HomeController
	should_descend_from Admin::BaseController
	it_should_behave_like 'administrative controllers'
end

shared_controller_examples.rb

shared_examples_for 'administrative controllers' do
	context 'access by administrative users' do
		before :each do
			setup_admin
			get :index
		end

		should_not_redirect_to { error_path(403) }
		should_succeed
	end

	context 'access by non-administrative users' do
		before :each do
			setup_user
			get :index
		end

		should_redirect_to { error_path(403) }
	end
end