Скачать или смотреть How to Effectively Test Http Requests that Update a Subject with Jest and Angular

Discover how to accurately test HTTP requests in Angular applications using Jest, ensuring that `observation$` and `_observations` are updated correctly with the latest data.
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This video is based on the question https://stackoverflow.com/q/77660405/ asked by the user 'Tomás Tubert SFC' ( https://stackoverflow.com/u/23101367/ ) and on the answer https://stackoverflow.com/a/77662078/ provided by the user 'Bastian Bräu' ( https://stackoverflow.com/u/2060981/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering the Testing of HTTP Requests in Angular with Jest

Testing is a crucial part of software development, especially when it comes to applications that rely heavily on asynchronous operations like HTTP requests. In this guide, we’ll tackle a common challenge faced by Angular developers: how to ensure that your HTTP request, which updates a subject, is functioning correctly using Jest. We’ll explore an actual scenario and offer a structured solution that you can apply in your own projects.

The Problem: Why Testing HTTP Requests Can Be Tricky

In Angular applications, it’s not uncommon to work with Observables and Subjects to handle asynchronous data. However, testing these can become complicated, especially when you expect an observable's value to change as a result of an HTTP request. For instance, consider a function designed to create a new odour by posting a request and updating a subject:

[[See Video to Reveal this Text or Code Snippet]]

In this scenario, we need to ensure that once the HTTP request is made, the subject observation$ updates to reflect the returned data. The challenge arises when attempting to validate this update in a unit test.

Step-by-Step Solution: Writing an Effective Test

To achieve reliable testing, follow these organized steps to structure your test effectively:

1. Mock the HTTP Client

Set up your test to use a mocked version of the HTTP client. This way, you can control the response returned without actually making a network request.

2. Subscribe to the Subject

Ensure that you subscribe to observation$ before you invoke the function that modifies it. This will ensure that you can check its value after the function completes.

3. Use Promises for Asynchronous Assertions

Instead of relying on subscriptions that may behave unexpectedly, opt for using promises in your tests. This approach improves clarity about whether your assertions will run and ensures they are processed at the right time.

4. Example Test Code

Here’s how you could implement the test:

[[See Video to Reveal this Text or Code Snippet]]

5. Identify BehaviorSubject

Ensure that observation$ is defined as a BehaviorSubject. This way, you can retrieve the last emitted value at any point, which helps avoid issues related to the timing of subscriptions.

Conclusion: Testing Made Simple

By following the structure laid out in this post, you can simplify the process of testing HTTP requests in your Angular applications. Using Jest effectively will not only make your tests more reliable but also significantly enhance your application’s robustness. Don’t shy away from diving deep into the asynchronous nature of JavaScript—embrace it and master the art of testing!

If you have any questions about Angular or testing, feel free to leave a comment below. Happy coding!