I've just submitted a rails patch http://dev.rubyonrails.org/ticket/11091
This patches actionpack/lib/action_controller/integration.rb so that post and put requests automatically get turned into multipart form submission requests if they have a parameter or parameters which are instances of TestUploadedFile.
This allows file uploading to be tested in integration controllers. This is a new answer tohttp://dev.rubyonrails.org/ticket/4635 which has been open for 2 years. There are three differences between the two year old patch and this one.
1) This patch includes a test 2) Instead of a separate multi_part_post method, this patch makes normal post and put requests (as well as post_via_redirect, and put_via_redirect work for muitpart posting. The ability to work with both post and put seems important for RESTful purposes. 3) It was just built against the curent edge Rails.
Please have a look if interested and verify the patch, looking for +1s on the Rails Trac