gistfile1.txt

Paperclip - Factory_Girl for Rails 3 beta 4 

    Factory.define :contacts_short_csv, :class => 'CsvFile' do |f|
      include ActionDispatch::TestProcess
      f.csv   { fixture_file_upload( 'files/contacts_short.csv.upload', 'text/csv') }
      f.account_id { 1 }
    end

My model is 

    class CsvFile < ActiveRecord::Base
      include Paperclip
      has_attached_file :csv
    end

The CSV file is actually under test/fixtures/files/ and since they are not real fixture data, but actual CSV data for testing the data import process, I had to rename them as .csv.upload otherwise Rails's test will try to populate the test databases with them (and fail miserably) 

I'm using Rails 3b4, with latest paperclip 61f74...eed69-master