<% Layout.testdrivelink %>
render a link to testdrive if the layout is *not* the currently active layout

Sourcecode in Layout/macros.js:
1:   function testdrivelink_macro(param) {
2:      if (this.isDefaultLayout())
3:         return;
4:      Html.link({href: this.href("startTestdrive")},
5:                param.text ? param.text : getMessage("Layout.test"));
6:      return;
7:   }