AngularJS unit test controller with only private functions - angularjs

Question

I have following controller that has only private functions. I am struggling to test this controller. Shall I test if it is doing $emit, since the ImageService has been tested? How do I test $emit in this case? Or shall I test if it is calling the ImageService.fetchImageStacks method? In this case, how do I trigger init function?
(function (angular, global, undefined) {
'use strict';
var ImageController = {};
ImageController.$inject = [
'$rootScope',
'$log',
'ImageService'
];
ImageController = function (
$rootScope,
$log,
ImageService
) {
var getImageStacks = function() {
ImageService
.fetchImageStacks()
.success(function (result) {
ImageService.setImageStacks(result);
$rootScope.$emit('rootScope:imageStacksUpdated', result);
})
.error(function (){
$log.error('Failed to get imageStackInfo file.');
});
};
var init = function () {
getImageStacks();
};
init();
return {
getImageStacks: getImageStacks
};
}
angular.module('myApp')
.controller('ImageController', ImageController);
})(angular, this);

Answer 1

You shouldn't be testing private/internal methods that are not available to the outside world(imho).
Some resources on the subject (for & against):
http://www.peterprovost.org/blog/2012/05/31/my-take-on-unit-testing-private-methods/
http://www.quora.com/Should-you-unit-test-private-methods-on-a-class
http://henrikwarne.com/2014/02/09/unit-testing-private-methods/
Should Private/Protected methods be under unit test?
Should I test private methods or only public ones?
With that said, you are exposing getImageStacks on the controller - so it isn't a private method. If you were to log out the result of instantiating the controller in your test suite, you should see something of the sort:
{ getImageStacks: function }
(init() in your case, is just an alias for getImageStacks (aka there is no need for the init method - you could just call getImageStacks and be done with it)).
Anyway, to write some tests;
First of, you should stub out the ImageService as we are not interested in the internal implementation of said service, we are only ever interested in the communication going from the controller to the service. A great library for stubbing/mocking/spying is sinonjs - get it, you won't regret it.
In the beforeEach I would suggest you do something like this:
// Stub out the ImageService
var ImageService = {
fetchImageStacks: sinon.stub(),
setImageStacks: sinon.stub()
};
var $scope, instantiateController;
beforeEach(function () {
// Override the ImageService residing in 'your_module_name'
module('your_module_name', function ($provide) {
$provide.value('ImageService', ImageService);
});
// Setup a method for instantiating your controller on a per-spec basis.
instantiateController = inject(function ($rootScope, $controller, $injector) {
ctrl = $controller('ImageController', {
$scope: $rootScope.$new(),
// Inject the stubbed out ImageService.
ImageService: $injector.get('ImageService')
});
});
});
Now you have a stubbed out ImageService to test calls against, and a method to instantiate your controller with the dependencies passed into it.
Some example specs you can run;
it('calls the ImageService.fetchImageStacks method on init', function () {
instantiateController();
expect(ImageService.fetchImageStacks).to.have.been.calledOnce;
});
it('calls the ImageService.setImageStacks on success', inject(function ($q, $timeout) {
ImageService.getImageStacks.returns($q.when('value'));
instantiateController();
$timeout.flush();
expect(ImageService.setImageStacks).to.have.been.calledOnce.and.calledWith('value');
}));
I hope that will suffice and answer your questions on;
If/when you should/shouldn't test internal implementation.
How to test the initialisation of the controller.
How to test methods of an injected service.