$ cat app/controllers/welcome_controller.rb
class WelcomeController < ApplicationController
  include OpenidUtility

  def complete
    real_user = 1
    redirect_to :controller => :items
  end
end

$ cat lib/openid_utility.rb
module OpenidUtility
  # Get the OpenID::Consumer object.
  def consumer
    # Create the OpenID store for storing associations and nonces
    #store =  ActiveRecordOpenIDStore.new
    store_dir = Pathname.new(RAILS_ROOT).join('tmp').join('openid-store')
    store = OpenID::Store::Filesystem.new(store_dir)

    return OpenID::Consumer.new(session, store)
  end
end

$ cat spec/controllers/welcome_spec.rb
require File.dirname(__FILE__) + '/../spec_helper'

describe WelcomeController do

  it "should login with a valid openid credential" do
    controller.should_receive(:real_user=)
    get 'complete'
    response.should redirect_to("http://test.host/items")
  end
end

$ rake spec:controllers
(in /home/donp/src/ruby/rails/catmystuff)
F

1)
Spec::Mocks::MockExpectationError in 'WelcomeController should login with a valid openid credential'
Mock 'WelcomeController' expected :real_user= with (any args) once, but received it 0 times
/home/donp/src/ruby/rails/catmystuff/vendor/plugins/rspec_on_rails/lib/spec/rails/example/behaviour/controller_example_group.rb:211:in `should_receive'

Finished in 0.637452 seconds

1 example, 1 failure
rake aborted!
Command ruby -I"/home/donp/src/ruby/rails/catmystuff/vendor/plugins/rspec/lib" "/home/donp/src/ruby/rails/catmystuff/vendor/plugins/rspec/bin/spec" "spec/controllers/welcome_spec.rb" --options "/home/donp/src/ruby/rails/catmystuff/spec/spec.opts" failed