Rails的fixture文件在传递给YAML解析之前先用ERB解析，这样一来我们就可以使用Ruby代码动态生成测试数据，而不用一条数据一条数据的写了:

<% 1.upto(50) do |number| %>
child_post_<%= number %>:
  id: <%= number + 3 %>
  title: This is auto-generated reply number <%= number %>
  body: We're on number <%= number %>
  created_at: 2006-01-30 08:03:56
  updated_at: 2006-01-30 08:03:56
  <%# Randomly choose a parent from a post we've already generated -%>
  parent_id: <%= rand(number - 1) + 1 %>
  user_id: <%= rand(5) + 1 %>
<% end %>

我们还可以定义一些helper方法:

<%
  def today
    Time.now.to_s(:db)
  end
  def next_week
    1.week.from_now.to_s(:db)
  end
  def last_week
    1.week.ago.to_s(:db)
  end
post_from_last_week:
  id: 60
  title: pizza
  body: Last night I had pizza. I readlly liked that story from AWDWR.
  created_at: <%= last_week %>
  updated_at: <%= last_week %>
  user_id: 1
post_created_in_future_should_not_display:
  id: 61
  title: Prognostication
  body: I predict that this post will show up next week.
  created_at: <%= next_week %>
  updated_at: <%= next_week %>
updated_post_displays_based_on_updated_time:
  id: 62
  title: This should show up as posted today.
  body: blah blah blah
  created_at: <%= last_week %>
  updated_at: <%= today %>
  user_id: 2