module Extendable
  def extended(x)
    @variable = []
  end

  def test
    @variable << self
  end

  def result
    @variable
  end
end

class Testee1
  extend Extendable
  test
end

class Testee2
  extend Extendable
  test
end

p Testee1.result
p Testee2.result