使用FactoryGirl时，Paperclip :: Attachment作为字符串传递

I am trying to create a functional test for paperclip 3.1.2 on rails 3.2.6 using FactoryGirl 3.0 and when i pass the file attachment my controller receives a string which is the file location and not the Paperclip::Attachment object.I am trying to create a functional test for pap