Testing Durandal Viewmodel that makes http call

Engineers ViewModel

define(['plugins/http', 'plugins/dialog', 'durandal/app', 'viewmodels/locale', 'knockout'], 
  function (http, dialog, app, locale, ko) {
    //Note: This module exports an object.
    //That means that every module that "requires" it will get the same object instance.
    //If you wish to be able to create multiple instances, instead export a function.
    //See the "welcome" module for an example of function export.

    var engineersViewModel = function() {
        var self = this;

        var cachedRates = {};
        self.rates = ko.observableArray();

        self.loadRates = function(country) {
            // If the user picked a new country
            if (typeof country !== 'undefined' && country !== null && country !== "") {

                if (cachedRates[country]) {
                    self.rates(cachedRates[country]);
                } else {
                    // Get engineer rates from server
                    return http.get('api/Booking/EngineerRates').then(function(response) {
                        cachedRates[country] = response;
                        self.rates(response);
                    });
                }
            }
        };

    };

    return new engineersViewModel();
});

Testing and mocking get call

describe("Engineers ViewModel", function() {

    beforeEach(function() {
        spyOn(http, 'get').andCallFake(function (req) {
            var d = $.Deferred();
            d.resolve({foo: 'bar'}); // pass in data that should be returned
            return d.promise();
        });
    });

    it("When getRates is called twice for the same country, it should only retrieve data once", function() {

        return engineers.loadRates('US')
            .then(function() { return engineers.loadRates('US'); })
            .then(function() {
                expect(http.get.callCount).toBe(1);
        });
    });

});