Testing AngularJS: $resource

This is the fourth post taking a look at testing various aspects of AngularJS. Previously, I covered:

In this installment we'll take a look at what I do to isolate components from their use of the $resource service and why.

$resource

The $resource service provides a simple way to define RESTful API endpoints in AngularJS and get updated data without lots of promise handling unnecessarily obfuscating your code. If you have created a resource for a specific route, you can get the returned data into your scope as easily as this:

The $resource magic ensures that once the request returns, the data is updated. It's clever stuff and incredibly useful.

However, when testing components that use resources, I want to isolate the components from those resources. While I could use $httpBackend or a cache to manipulate what results the resource returns, these can be cumbersome to setup and adds unnecessary complexity and churn to unit tests1. To avoid this complexity, I use a fake that can be substituted for $resource.

spyResource

My fake $resource is called spyResource. It is not quite a 1-1 replacement, but it does support the more common situations one might want (and it could be extended to support more). Here it is.

First of all, it is just a function. Since it is part of my testing framework, there is no need to wrap it in some fancy AngularJS factory, though we certainly could if we wanted.

Second, it mimics the $resource service by returning a function that ultimately copies itself. This is useful because you do not necessarily have access to the instances of a resource that are created in your code before posting an object update to your RESTful API. By copying itself, you can see if the $save() call is made directly from the main spyResource definition, even if it was actually called on an instance returned by it because they share the same spies.

To use this in testing, the $provide service can be used to replace a specific use of $resource with a spyResource. For example, if you defined a resource called someResource, you might have:

Now, the fake resource will be injected instead of the real one, allowing us to not only spy on it, but to also ensure there are no side-effects that we have not explicitly set up.

Finally…

I have covered a very simple technique I use for isolating components from and spying on their usage of AngularJS resources. The simple fake resource I provided for this purpose can be easily tailored to cater to more complex scenarios. For example, if the code under test needs data from the get() method or the $promise property is expected in get() return result, the spy can be updated to return that data.

Using this fake resource instead of $httpBackend or a cache to manipulate the behavior of a real AngularJS resource not only simplifies the testing in general, but also reduces code churn by isolating the tests from the API routes that can often change during development.

As always, please leave a comment if you find this useful or have other feedback.

 

 


  1. API routes can often change during development, which would lead to updating $httpBackend test code so that it matches 

Testing AngularJS: Asynchrony

So far, we have looked at some techniques for testing simple AngularJS factories and directives. However, things are rarely simple when it comes to web development and one area that complicates things is that of asynchronous operations such as web requests, timeouts and promises.

Eventually, when writing AngularJS, you will rely on the $timeout, $interval, or $q services to defer an action by some interval or indefinitely using promises. I will not go very deep into their use here, you can read much of that on the AngularJS documentation, but since it is likely that you will use them, how do you test them? How do you test asynchronous code without horribly complex and unreliable tests?

$timeout

Consider this simple example where we have a controller that defers some action using $timeout.

Here we have a variable, started that is initialised to false and a deferred method that changes that value to true. A first stab at testing this might look a little like this:

Unfortunately, such a test will not pass because the deferred code would not execute until after the expectation was tested. We can mitigate this by using some AngularJS magic provided by the ngMock module.

The ngMock module adds the $timeout.flush() method so that code deferred using $timeout can be executed deterministically1. The test can therefore be modified such that it passes by adding the highlighted line below.

$q

For promises that were deferred using $q (including the promise returned from using $interval), we can use $scope.$apply() to complete a resolved or rejected promise and execute any code depending on that promise.

In the following contrived example, we have a controller with a start() method that returns a promise and a started() method that resolves that promise.

The preceding test validates our controller and its promise. If you delete the highlighted line, you would see that the test fails because the resolved promise is never completed.

Finally…

In this post, we have taken a brief look at how AngularJS supports the testing of asynchronous code execution deferred using $timeout, $interval, or $q. The ability to synchronously control otherwise asynchronous actions not only allows us to test that deferred code, but also to prevent it executing at all. This can be incredibly useful when isolating different parts of our code by reducing how much of it has to run to validate a specific method.

Of course, quite often, a promise is only resolved after an HTTP request responds or fails, such as when using $resource. When writing unit tests, you may not have nor want the luxury of a back-end server that responds appropriately to test requests. Instead, you either want to fake out $resource, or fake out and validate the HTTP requests and responses2. In upcoming posts, we'll look at a simple $resource fake for the former and the special $httpBackend service that AngularJS provides for the latter. Until then, please leave your comments.


  1. The flush() method even takes a delay parameter to control which timeouts will execute and a similar method exists for $interval 

  2. The requests that you expect your code to make and the responses that your code expects to receive – or doesn't, as the case may be 

Track pending web requests with AngularJS

Navigation Guard

In the previous two posts (here and here), I covered the AngularJS factory, saNavigationGuard that I had created. This factory provides a simple way to guard against inconvenient page navigation in our Angular applications. However, up until now, I have not demonstrated one of the coolest uses for this. Before we look at this awesome use of saNavigationGuard, let us take a short trip into late last year.

I was getting started on my first big project with AngularJS and I had added a busy indicator to my user experience. To control when the indicator was active, I used a counter. This counter was incremented and decremented before and after using Angular resources. It was a nest of promises and error handlers, just to make sure the counter worked properly. I was not entirely happy with it but it was the best I could work out from my knowledge of Angular and JavaScript, so I submitted a pull request. My colleague reviewed the work and, looking at the busy indicator and the code to control the counter, stated, "there must be a better way."

I did not know at the time, but he was right, there is a better way and it uses an Angular feature called "interceptors".

Interceptors

Interceptors provide hooks into web requests, responses and their errors allowing us to modify or handle them in different ways. They are provided via an AngularJS provider such as a factory or service and injected into the $httpProvider using config as follows.

In this snippet, the name of the interceptor, saHttpActivityInterceptor, is added to the array of interceptors on $httpProvider.

The interceptor itself is a little more complex.

The interceptor factory returns an object that, in this case, has three methods: request, response and responseError. A fourth method, requestError, can also be included in interceptors if needed. Before returning our interceptor, the interceptor factory registers a guardian with saNavigationGuard that will guard against navigation if the pendingRequestsCounter is greater than zero.

The interceptor monitors requests and responses. On each request, the request method is checked, if it is POST, PUT or DELETE, the pendingRequestsCounter variable is incremented by one and the request is tagged to indicate it is being tracked. We flag it so that we know to pay attention when the corresponding response or response error occurs. In the response and response error handlers, we decrement our counter based on the tracking flag and the method.

Finally…

The outcome of using this interceptor is that if the user tries to navigate away from the page after a request has been made but before its response has been received, they will see a message asking them to consider postponing the navigation.

In the next post, we will look at testing both this interceptor and the saNavigationGuard functionality using my preferred combination of jasmine, CoffeeScript and jasmine-given.

As always, please consider leaving a comment if you have found this post useful or have any alternatives.