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
	describe 'before_filter' do
		it 'should respond to :require_admin' do
			controller.should respond_to(:require_admin)
		end
	end
	
	describe 'not redirecting when user is an admin' do
		before :each do
			user = stub_model(User)
			user.should_receive(:is_administrator?).and_return(true)
			User.should_receive(:find_by_id).and_return(user)
			get '/admin/home/index'
		end
		
		should_not_redirect_to { error_path(403) }
	end

	describe 'redirecting when user is not an admin' do
		before :each do
			user = stub_model(User)
			user.should_receive(:is_administrator?).and_return(false)
			User.should_receive(:find_by_id).and_return(user)
			get '/admin/home/index'
		end
		
		should_redirect_to { error_path(403) }
	end
end