How to test Storybook components in Angular applications

A step-by-step tutorial

To better understand the Applitools Storybook SDK for Angular, here is a tutorial on how to build a small AngularJS application from scratch, adding some Storybook stories, and then finally performing visual regression testing using the Applitools SDK to generate snapshots for us to view and analyze.

You can find the source code for this article on GitHub by following this link storybook-angular-applitools repo.

Create Angular 7 App using the latest CLI

Create the ContentEditable Component

The HTML fragment above renders in the browser as an editable area that users can click and enter any text or HTML.

Create a new component file and add the following markup to contenteditable.component.html file:

Next, add the code below to the contenteditable.component.ts file:

The component is straightforward and follows the best practices in building a ControlValueAccessor. It defines a single @Input() property to allow the consumer of this component to control its styling.

If you want to fully understand how ControlValueAccessor works in Angular check out Max’s article titled Never again be confused when implementing ControlValueAccessor in Angular.

Next, add the following HTML snippet to the app.component.html file:

Define the styles() method inside the AppComponent class:

And now run the application. You should see something similar to this below.

You can start typing in the yellow editable rectangle and you will see whatever you type underneath.

Let’s switch gears and add Storybook to the application.

Add Storybook packages

Open the src/app/tsconfig.app.json file and make sure the exclude property has the following values:

Open the .storybook/tsconfig.json file and paste the following:

Create and run a few Storybook stories

The first story renders the ContentEditable component with a yellow background. While the second renders the component with a red background.

Run the Storybook tool to view and test your stories by issuing the following CLI command:

You should be able to see something similar to this:

Now that we are sure the Storybook stories are up and running, let’s set up Applitools to use these stories and run our visual automated tests.

Add and run Applitools Storybook SDK for Angular

Make sure to grab an Applitools API Key and store it on your machine. For a complete tutorial on how to install and run Applitools Storybook SDK for Angular, you may check this link: Storybook Angular Tutorial.

To run the Storybook stories and send the snapshots to the Applitools Server, issue the following command:

The command simply opens the Storybook stories, runs them one by one, and then sends all the DOM snapshots to the Applitools Server.

Let’s have a look at the test results inside Applitools Test Manager.

Review test results on Applitools Test Manager

For a detailed look at the Applitools Test Manager, you can check this article: Applitools — The automated visual regression testing framework.

The results for running the Storybook tests show the following:

The test manager lists the test runs or batches (as referred to by Applitools) on the left- hand side. Clicking on any of the batches displays all of the snapshots for all of the Storybook stories in your application.

Click on the first snapshot (the red color) to expand and review it in detail:

A rich toolbox is available to zoom in/out on the snapshot and compare this snapshot to any previously taken, known as the baseline. In this case, since this is the first time we are running the stories, there won’t be any baseline set. Therefore, Applitools Test Manager sets these snapshots as a baseline for upcoming regression test cycles.

Next, we’re going to simulate what happens when we have a visual regression in one of our components. To do this most easily, we’ll change one of our Storybook stories to render our component in a way that will be different from the baseline images we took earlier. Then, when we re-run the visual testing, we should see a discrepancy appear that we’ll have to resolve.

To do this, let’s assume that the story named in the red background above, has the ngModel value changed and now reads as follows:

Now run this command:

The command gives you a detailed test result every time you run it. Check the following results:

Running the second story fails, as expected because we changed the content that was initially displayed inside the ContentEditable component. The test result output provides you with a link to check the discrepancies online. Click on the link to open the issues directly in the Applitools Test Manager:

A new batch is displayed on the left-hand side with a status of Unresolved. The Unresolved status indicates that the Applitools Test Manager discovered a discrepancy between the two test runs. This will require your input in order to resolve the discrepancy. Either approve the difference, and create a new baseline, or reject it to keep the original baseline.

Notice the blue square above indicating the Not Equal sign. This means the second snapshot test run has some differences to the first test run snapshot (the baseline). Clicking on the first snapshot reveals the differences between both snapshots. The current one and the baseline. The differences in content are highlighted in blue. You can also compare the new snapshot with the baseline by selecting both:

This should display both side by side and all differences are highlighted for you. You may spend more time at the Applitools Test Manager to explore all the rich features provided for you to do a thorough analysis on running the story tests.

Conclusion

You can grab the code for this article by cloning the repository on Github.

So how are you going to test the Storybook components in your Angular apps?

This post was written by Bilal Haidar, a mentor with ThisDot

Originally published at Applitools Blog.

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