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I would like to hear other people's opinion on how I unit tested a functionality in a Backbone Model. As you see below, the code under test, upon being called to toggle, toggles its completed state and saves the new state:

// js/models/todo.js

  var app = app || {};

  // Todo Model
  // ----------
  // Our basic **Todo** model has `title` and `completed` attributes.

  app.Todo = Backbone.Model.extend({

    // Default attributes ensure that each todo created has `title` and `completed` keys.
    defaults: {
      title: '',
      completed: false
    },

    // Toggle the `completed` state of this todo item.
    toggle: function() {
      this.save({
        completed: !this.get('completed')
      });
    }

  });

To unit test this, as you can see below, I stub Backbone.sync method and make sure that the Model is saved with the correct state:

describe("todo", function() {
    it("should save the toggled completed state", function() {
        var stub = sinon.stub(Backbone, "sync", function(method, model) {
            expect(model.get("completed")).to.equal(true);
        });

        var todo = new app.Todo({completed: false});

        todo.toggle();

        expect(stub.calledOnce).to.equal(true);

        Backbone.sync.restore();
    });
});
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I'm not really familiar with mocha. If I understand correctly, the true and false values here closely releated, in the sense that they should be opposites:

var stub = sinon.stub(Backbone, "sync", function(method, model) {
    expect(model.get("completed")).to.equal(true);
});

var todo = new app.Todo({completed: false});

In that case, to avoid mistakes, it would be better to include that logic in the code, for example:

var initial_state = false;
var stub = sinon.stub(Backbone, "sync", function(method, model) {
    expect(model.get("completed")).to.equal(initial_state);
});

var todo = new app.Todo({completed: !initial_state});

And maybe add another test for the inverse, for initial_state = true.


Instead of this:

var todo = new app.Todo({completed: false});
todo.toggle();

Since you only use the todo instance once, I would combine the two lines to shorten the code:

new app.Todo({completed: false}).toggle();

Instead of this .to.equal(true):

expect(stub.calledOnce).to.equal(true);

I think it would be more natural (and shorter) with .to.be.ok():

expect(stub.calledOnce).to.be.ok();
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