test.js

  test('Do not allow duplicate models (with nonstandard id) to be `add`ed or `set`', function() {
    var Stooge = Backbone.Model.extend({
        parse: function(a) {
            var attrs = {};
            attrs._id = a.__id;
            return attrs;
        }
    });
    Stooge.prototype.idAttribute = '_id';
    var StoogeCollection = Backbone.Collection.extend({model: Stooge}),
        c = new StoogeCollection();
    c.add([{__id: 1}, {__id: 1}]);
    equal(c.length, 1);
    equal(c.models.length, 1);
    c.set([{__id: 1}, {__id: 1}]);
    equal(c.length, 1);
    equal(c.models.length, 1);
  });