mocking an error/exception in rspec (not just its type)

require 'mechanize'

class Foo

  def some_method
    begin
      do_some_stuff
    rescue WWW::Mechanize::ResponseCodeError => e
      if e.response_code.to_i == 503
        handle_the_situation
      end
    end
  end

end

describe "Foo" do

  it "should handle a 503 response" do
    page = stub(:code=>503)
    foo = Foo.new
    foo.should_receive(:do_some_stuff).with(no_args)\
    .and_raise(WWW::Mechanize::ResponseCodeError.new(page))
    foo.should_receive(:handle_the_situation).with(no_args)
    foo.some_method
  end

end