image_uploader.rb

class ImageUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick

  process :convert => 'png'
  process :resize_to_fit => [600, 600]
  
  version :thumb do
    process :convert => 'png'
    process :resize_to_fill => [100, 100]
  end
  
  version :tiny do
    process :convert => 'png'
    process :resize_to_fill => [45, 45]
  end

  def cache_dir
    "#{Rails.root}/tmp/uploads"
  end
  
  def extension_white_list
    %w(jpg jpeg gif png bmp)
	end
  
  def filename
    "#{mounted_as}.png"
  end
  
  def max_file_size
    5242880
  end

  def store_dir
    "#{model.class.to_s.downcase.pluralize}/#{model.username}"
  end
end

image_uploader_spec.rb

require 'spec_helper'
include CarrierWave::Test::Matchers

describe ImageUploader do
 before :all do
   @user = Factory(:user)
   ImageUploader.enable_processing = true
   @uploader = ImageUploader.new(@user, :avatar)
   @uploader.store!(File.open("#{Rails.root}/features/files/thumb_avatar.jpg"))
 end

 after :all do
   @uploader.remove!
   ImageUploader.enable_processing = false
 end

 describe 'the large version' do
    it "should scale down a landscape image to fit within 600 by 600 pixels" do
      @uploader.should be_no_larger_than(600, 600)
    end
  end

 describe 'the thumb version' do
   it "should scale down a landscape image to be exactly 100 by 100 pixels" do
     @uploader.thumb.should have_dimensions(100, 100)
   end
 end

 describe 'the tiny version' do
   it "should scale down a landscape image to be exactly 45 by 45 pixels" do
     @uploader.tiny.should have_dimensions(45, 45)
   end
 end
end