gistfile1.rb

require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')
require File.expand_path(File.dirname(__FILE__) + '/../spec_helpers/controller_behaviors')

describe SomeController do
  stub_all_filters!
  
  describe "#foo" do
    def do_get
      get :foo
    end
    
    it "should do something" do
      controller.send(:instance_variable_set, "@bar", "here's bar")
      do_get
    end
  end
end

class SomeController < ApplicationController
  def foo
    p "need to do something with #{@bar}"
  end
end