add spec for callbacks

spec/uploader/callbacks_spec.rb

@@ -0,0 +1,21 @@
+require 'spec_helper'
+
+describe CarrierWave::Uploader do
+  describe 'callbacks' do 
+    before do
+      @uploader_without_callbacks = Class.new(CarrierWave::Uploader::Base)
+      @uploader_with_callbacks    = Class.new(CarrierWave::Uploader::Base) do 
+        before :cache, :before_cache 
+        after  :cache, :after_cache 
+      end
+    end
+
+    it 'should only be inherrited' do 
+      @uploader_without_callbacks._before_callbacks[:cache].should == CarrierWave::Uploader::Base._before_callbacks[:cache]
+      @uploader_without_callbacks._after_callbacks[:cache].should == CarrierWave::Uploader::Base._after_callbacks[:cache]
+
+      @uploader_without_callbacks._before_callbacks[:cache].should_not == @uploader_with_callbacks._before_callbacks[:cache]
+      @uploader_without_callbacks._after_callbacks[:cache].should_not == @uploader_with_callbacks._after_callbacks[:cache]
+    end
+  end
+end