test.rb

module Security
  module Bouncer
    THE_LIST = %w(john)

    def enter(name)
      raise "Sorry #{name}, you're not on the list" unless THE_LIST.include?(name)
      puts "Hey #{name}, come on through."
      super(name)
    end
  end

  def self.prepended(base)
    class << base
      prepend Bouncer
    end
  end
end

module Club
  prepend Security

  def self.enter(name)
    puts "#{name} has entered the building"
  end
end

class ClubSimulator
  @queue = %w(john john amy john)
  def self.run
    @queue.each do |name|
      begin
        Club.enter name
      rescue Exception => e
        puts e.message
      end
    end
  end
end

ClubSimulator.run