gistfile1.js

requirejs.rollback = function() {
  for(var entry in this.previousEntries) {
    if (this.previousEntries[entry]) {
      registry[entry] = this.previousEntries[entry];
    } else {
      delete registry[entry];
    }
  }
};

requirejs.define = function(entry, deps, callback) {
  if (this.previousEntries[entry]) {
    throw 'cannot define twice';
  } else {
    this.previousEntries[entry] = registry[entry];
    registry[entry] = { deps: deps, callback: callback };
  }
};

module('validator class lookup order', {
  setup: function() {
    requirejs.previousEntries = {};
  },
  teardown: function() {
    requirejs.rollback();
  }
});