included 타이밍에 변경한걸 되돌리기 힘들어서 결국 매번 새로만들기로 했어요.

lib_yahoo.rb

module Yahoo
  self.included(base)
    base.messages << :yahoo
  end
end

spec_lib_yahoo_spec.rb

require 'spec_helper'
 

describe Yahoo do
  let(:yahoo_included_test_object) do
    class_with(Yahoo).new
  end
  let(:test_object) do
    TestBase.new
  end
  it { yahoo_included_test_object.class.messages.should include(:yahoo)}
  it { test_object.class.messages.should_not include(:yahoo)}
end

spec_support_include_helper.rb

class TestBase
  def self.messages
    @messages ||= []
  end
end

def class_with(*modules)
  Class.new(TestBase) do
    include modules
  end
end