Mocked Backbone.ajax

spy-ajax.js

import $ from 'jquery';
import Backbone from 'backbone';

export var ajaxSpy;

export default function spyAjax() {
    var deferreds;
    beforeEach(function() {
        deferreds = [];
        ajaxSpy = spyOn(Backbone, 'ajax').and.callFake(({success, error}) => {
            if(deferreds.length === 0) {
                throw new Error('Unexpected request!');
            }
            const deferred = deferreds.shift();
            deferred.done(success);
            deferred.fail(error);
            return deferred;
        });
    });

    afterEach(function() {
        if(deferreds.length > 0) {
            throw new Error('There unfulfilled requests');
        }
    });

    function expectDeferred() {
        const deferred = $.Deferred();
        deferreds.push(deferred);
        return deferred;
    }
    return expectDeferred;
}

test.js

import {Model} from 'backbone';
import spyAjax, {ajaxSpy} from './spy-ajax';

class TestModel extends Model {
  url = '/api';
  
  fetchAll() {
    return Promise.all([
      fetchA(),
      fetchB()
    ]);
  }
}

describe('ModelTest', function() {
  const expectAjaxRequest = spyAjax();
  
  it('should fetch model', function() {
    const model = new TestModel();
    const deferred = expectAjaxRequest();
    model.fetch();
    deferred.resolve({key: 'value'});
    expect(model.get('key')).toBe('value');
  });
  
  it('should save model', function() {
    const model = new TestModel();
    const deferred = expectAjaxRequest();
    model.save('key', 'value');
    deferred.resolve();
    expect(ajaxSpy).toHaveBeenCalledWith(joc({method: 'POST', url: '/api'}))
    expect(model.get('key')).toBe('value');
  });
  
  it('should make cascade fetch', function() {
    const deferredA = expectAjaxRequest();
    const deferredB = expectAjaxRequest();
    const model = new TestModel();
    model.fetchAll();
    expect(ajaxSpy.calls.count()).toBe(2);
  })
});