Adding value to hash in ruby on rails

I have a problem with adding a new key and value to a hash in ruby on rails. The method looks like this with two debug prints and should simply add the provider key with index + 1 as value, in order to access the provider with the right ID later.

search_result.each_with_index do |articles, index|
  puts "merge-articles: #{articles}"
  articles.each{ |article| article[:provider] = index + 1;}
  puts "merge-articles(later): #{articles}"
end                                        

I get those output from the puts, which look quite good to my mind:

merge-articles: [{:ean=>"9780234474278", :author=>"Dan Brown", :name=>"The Da Vinci Code", :price=>19.65, :image=>"www.google.de/image.png"}]
merge-articles(later): [{:ean=>"9780234474278", :author=>"Dan Brown", :name=>"The Da Vinci Code", :price=>19.65, :image=>"www.google.de/image.png", :provider=>2}]

The Spec which only tests if the keys exist gets this error:

 Failure/Error: HomeController.merge(@no_same_items_merge).each do |item|
 TypeError:
   can't convert Symbol into Integer
 # ./app/controllers/home_controller.rb:41:in `[]='
 # ./app/controllers/home_controller.rb:41:in `block (2 levels) in merge'
 # ./app/controllers/home_controller.rb:41:in `each'
 # ./app/controllers/home_controller.rb:41:in `block in merge'
 # ./app/controllers/home_controller.rb:39:in `each'
 # ./app/controllers/home_controller.rb:39:in `each_with_index'
 # ./app/controllers/home_controller.rb:39:in `merge'
 # ./spec/controllers/home_controller_spec.rb:104:in `block (5 levels) in <top (required)>'

Edit: The RSpec test looks like this:

    it "should return an array of right formatted hashes" do
      HomeController.merge(@no_same_items_merge).each do |item|
        item.should have_key(:name)
        item.should have_key(:ean)
        item.should have_key(:author)
        item.should have_key(:description)
        item.should have_key(:url)
        item.should have_key(:prices)
        item.should have_key(:images)
      end
    end   

Thanks for your help!