如何在Rails的功能测试中测试Cookie状态?

这是适用于Rails 2.3.8的代码(注释掉的行使测试无法通过):

test 'cookie testing should work' do
  @request.cookies['foo'] = 'Foo'
  # cookies['foo'] = 'Foo'
  # this does not work to: CGI::Cookie.new('foo', 'bar')
  get :index # does: cookies[:foo] = (cookies['foo'] || "") + " bar!" 
  # the cookie key in the controller can by a symbol, but not in the test
  assert_response :success
  assert_not_nil cookies['foo'], "Cookie with foo key should not be nil. Debug: Cookies=#{cookies.inspect}"
  assert_equal "Foo bar!", cookies['foo'], "Debug: Cookies=#{cookies.inspect}"
  # assert_not_nil @cookies['foo'], "Cookie with foo key should not be nil. Debug: Cookies=#{@cookies.inspect}"
  # assert_not_nil @request.cookies['foo'], "Cookie with foo key should not be nil. Debug: Cookies=#{@request.cookies.inspect}"
  # assert_equal "Foo bar!", @request.cookies['foo'], "Debug: Cookies=#{@request.cookies.inspect}"
end

我花了很长时间寻找答案。