should_receive.rb

class Object

  def should_receive!(sym, opts={}, &block)
    objx = Object.new

    @__rspec_obj__ ||= Object.new

    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

spec.rb

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