var Lightbulb = function () {
    this.isOn = false;
  },
  lightbulb = new Lightbulb();

Lightbulb.prototype.toggle = function () {
  this.isOn = !this.isOn;
  return this.isOn;
};

test('lightbulb sin IIFE.', function () {
  equal(lightbulb.toggle(), true, 'Lightbulb retorna on.');
  equal(lightbulb.toggle(), false, 'Lightbulb retorna off.');
});