Let activerecord handle the picture upload in factories

spec/factories/sponsors.rb

@@ -9,11 +9,10 @@ FactoryGirl.define do
     sponsorship_level
 
     after(:create) do |sponsor|
-      logo = "#{1 + rand(13)}.png"
-      uploader = PictureUploader.new(sponsor, :picture)
-      File.open("spec/support/logos/#{logo}") { |f| uploader.store!(f) }
-      sponsor.logo_file_name = logo.to_s
-      sponsor.save
+      File.open("spec/support/logos/#{1 + rand(13)}.png") do |file|
+        sponsor.picture = file
+      end
+      sponsor.save!
     end
   end
 end