title: Test::Unit should equivalent of RSpec should_receive
body: <p>I am writing some unit tests for my Ruby on Rails application. I would like to test that my model received a message to a particular method. In RSpec this is done with the <code>should_receive</code> incantation. </p>
  
  <p>Is there an equivalent to Test::Unit that can do the same? If Test::Unit cannot do it, is there a tool I can use in concert with it to get that functionality?</p>