如何让黄瓜显示完整(rails)错误信息？

似乎cuke没有显示完整的错误消息(至少在模板中出现问题时),这使得很难找到问题.

以下是它输出的一些错误:

 
...
    And I am on checkout page                                   # features/step_definitions/webrat_steps.rb:6
      You have a nil object when you didn't expect it!
      The error occurred while evaluating nil.items (ActionView::TemplateError)
      features/manage_orders.feature:9:in `And I am on checkout page'
...

以下是rails在浏览器中重现相同问题时显示的内容:

Showing app/views/cart/show.erb where line #46 raised:

You have a nil object when you didn't expect it!
The error occurred while evaluating nil.items

Extracted source (around line #46):

43: 
44: 
45: <% ths = %w{th_title th_price th_subtotal th_quantity}.collect {|th| t th.intern} %>
46: <% table(@cart.items, ths) do |cart_item, style| -%>
47:   
48:       <%=h cart_item.title %>
49:       <%=number_to_currency cart_item.price %>

前者有点太整洁了.在cucumber.log中也没有例外.我的模板有很少的部分和布局.没有线索,相当调查.

是否有任何秘密插头来获取黄瓜显示完整错误？

正确的答案(感谢cuke google group)正在--backtrace运行黄瓜时使用选项.