test.rb

module Tester
  def Tester.hello
    print 'hello'
  end

  extend Module.new {
    def world
      print 'world'
    end
  }

  extend Module.new {
    def world
      print 'cruel'
      super
    end
  }
end

Tester.extend Module.new {
  def world
    print 'lonely'
    super
  end
}