title: How can I add more data to assertion message?
body: <p>Spock has great assertion support. But I've got one problem - I wanna add more context data (for example url of the checked page) to assertion info.<br>
   I've tried
  <code>assert a == b, [context]</code> but in this case Spock doesn't print <code>a</code> and <code>b</code> values </p>