node/test/mjsunit/test-promise-cancel.js

process.mixin(require('./common'));
events = require('events');

var promise = new events.Promise();
var cancelled = false;
promise.addCancelback(function(){
  if(cancelled){
    assert.ok(false, "promise should not cancel more than once");
  }
  cancelled = true;
});
promise.cancel();
promise.cancel();