configuration.rb

include 'singleton'
class Configuration
  include Singleton
 
  def self.run
    yield Configuration.instance
    
    post_config_process
  end
end

configuration_spec.rb

describe Configuration do
  describe 'self.run' do
    it 'yields the Configuration instance' do
      lambda do
        Configuration.run do |c|
          #it yields the right thing
          c.should == Configuration.instance
          throw :it_yielded
        end
      end.should throw_symbol(:it_yielded) #proves it yielded
    end
  end
end