对生成的对象调用的测试方法

我有以下控制器测试用例:

def test_showplain
  Cleaner.expect(:parse).with(@somecontent)
  Cleaner.any_instance.stubs(:plainversion).returns(@returnvalue)

  post :showplain, {:content => @somecontent}

end

这是控制器代码:

def showplain
   Cleaner.parse(params[:content]) do | cleaner |
      @output = cleaner.plainversion
   end
end

class Cleaner

   ### other code and methods ###

   def self.parse(@content) 
     cleaner = Cleaner.new(@content)
     yield cleaner
     cleaner.close
   end

   def plainversion
      ### operate on @content and return ###
   end

end

同样,我也不知道如何可靠地测试“parse”方法提供的“cleaner”。有什么建议吗?