multi thread test

Hi All. I want to test by multi thread.(functional test) as below

* test class ItemControllerTest < ActionController::TestCase

  self.use_transactional_fixtures = false   POOL_SIZE = 5

  def setup     @connection = ActiveRecord::Base.remove_connection

ActiveRecord::Base.establish_connection(@connection.merge({:allow_concurrency => true, :pool => POOL_SIZE}))     activate_authlogic   end

  test "multi thread test" do     user = accounts(:one)     assert(AdAccountSession.create(user))     item = items(:one)     before_count = item.count     params = {:id =>, :count => 10}     threads = (1..5).map do do         10.times do           put :update, params         end       end     end     threads.each(&:join)   end   assert_equal before_count + 10 * 5, item.reload.count


* controller class ItemsController < ApplicationController   def update     count = params[:count]     id = params[:id]     update_sql = "UPDATE items SET count = count + #{count} WHERE id = #{id}"     Item.connection.update(update_sql)     redirect_to(@item, :notice => 'Item was successfully updated.')     return   end end

But raise error test_samaple(ItemsTransactionControllerTest): AbstractController::DoubleRenderError: Render and/or redirect were called multiple times in this action. Please note that you may only call render OR redirect, and at most once per action. Also note that neither redirect nor render terminate execution of the action, so if you want to exit an action after redirecting, you need to do something like "redirect_to(...) and return".

This error isn't raised in case of single thread(threads = (1..1).map do) How can I test by multi thread?

appreciate any help. Thank you Masaki.