testing listener of Backbone event

gistfile1.js

describe('when add event is fired on Todos collection', function() {
  before(function() {
    var init = this.TodoList.prototype.initialize;

    // spying event related method
    this.TodoList.prototype.initialize = function() {
      sinon.spy(this, 'renderOne');
      init.apply(this, arguments);
    };

    this.todoList = new this.TodoList({ el: '#main' });

    this.added = new Backbone.Model({ content: 'piyo' });
    this.todoList.collection.add(this.added);
  });

  after(function() {
    this.todoList.renderOne.restore();
  });

  it ('should render new TodoItem view', function() {
    this.todoList.renderOne.calledOnce.should.be.ok;
    this.todoList.renderOne.args[0][0].get('content').should.eql('piyo');
  });
});