Override this test runner with your own at app/views/sandbox_assets/test_runner/iframe.html.erb. The test to include is available at @tests.first:

• <%= link_to @tests.first, javascript_path(@tests.first) %>

And those stylesheets will be also included:

<% @stylesheets.each do |css| -%>
• <%= link_to css, stylesheet_path(css) %>
<% end -%>

Here is the source for this file (<%= __FILE__ %>):

<%= IO.read __FILE__ %>