title: Howto get a callback on JS function execution using a Spy
body: <p>I want to spy on a function, then execute a callback upon function completion/initial call.</p>
  
  <p>The following is a bit simplistic, but shows what I need to accomplish:</p>
  
  <pre><code>//send a spy to report on the soviet.GoldenEye method function
  var james_bond = sinon.spy(soviet, "GoldenEye");
  //tell M about the superWeapon getting fired via satellite phone
  james_bond.callAfterExecution({
      console.log("The function got called! Evacuate London!");
      console.log(test.args);
  });
  </code></pre>
  
  <p>Is it possible to do this in Sinon? Alternate libraries welcome as well if they solve my problem :)</p>