Perhapps you want to test a particular method on a class and really like the RSpec mock framework for tracking the ordering of the method calls for you. However you would really like not to have to provide stubs. You really want the methods to execute.

class Fing
  def bar
    puts " bar really called"
  end
  def bing
    puts " bing  really called"
  end
end

describe Fing do
  it "is a monkey" do
    b = Fing.new
    b.should_receive!(:bar).once.ordered
    b.should_receive!(:bing).once.ordered
    b.should_receive!(:bar).once.ordered
    b.bar
    b.bing
    b.bar
  end
end

Well we can monkey patch the Object class just like RSpec does and add a should_receive! method. This now uses RSpec to track the method calls but also passes the arguments to the real method calls.

class Object

    class ProxyObject

        attr_accessor :fake_class

        def to_s
            @fake_class.to_s
        end

    end

    def should_receive!(sym, opts={}, &block)

        @__rspec_obj__ ||= ProxyObject.new
        @__rspec_obj__.fake_class = self.class

        m = class<<self;self;end

        sym_old =  "__#{sym}__old__"

        # Generates for sym => :foo
        #
        #   alias :foo_old :foo
        #
        #   def foo *args, &block
        #       foo_old *args, &block
        #       @__rspec_obj__.send :foo, *args, &block
        #   end
        if not respond_to?("#{sym_old}".to_sym)
            m.class_eval <<-EOS, __FILE__, __LINE__
                    alias :#{sym_old} :#{sym}

                    def #{sym}  *args, &block 
                            #{sym_old} *args, &block
                            @__rspec_obj__.send :#{sym}, *args, &block
                    end
            EOS
        end
        @__rspec_obj__.should_receive(sym, opts, &block)
    end

end

I’m not sure if this is considered heretical in the world of mocks but it was a fun excercise in metaprogramming.