10 Angular Unit Testing Best Practices

Unit testing is an important part of the development process. Here are 10 best practices for unit testing Angular applications.

Angular unit testing is an essential part of the development process, and there are a number of best practices that can make it more effective. In this article, we’ll discuss 10 of those best practices, including things like using the Angular CLI, mocking dependencies, and using test-driven development. By following these best practices, you can make sure that your unit tests are comprehensive and effective, and that they’re helping you to build high-quality Angular applications.

1. Don’t test Angular framework functions

When you’re unit testing your Angular application, you’re testing the functionality of your code, not the functionality of the Angular framework itself. The Angular team has already done an excellent job of testing the Angular framework, so there’s no need for you to duplicate their efforts.

Instead, focus on testing the functionality of your code that calls into the Angular framework. For example, if you have a component that uses the Angular Router service to navigate to a different route, you would want to test that your component is calling the router service with the correct parameters.

By following this best practice, you’ll save yourself a lot of time and effort, and you can be confident that the Angular framework will work as expected in your application.

2. Test only your code

When you’re unit testing, you’re testing the functionality of your code in isolation. This means that you shouldn’t be testing the behavior of Angular itself, or any other third-party libraries that your code is using.

The reason for this is twofold. First, it’s out of scope. Your unit tests should only be concerned with the functionality of your own code. Second, it’s unnecessary. These dependencies are already well-tested by their respective maintainers, so there’s no need for you to duplicate their efforts.

3. Use the right tools

The Angular framework was designed with unit testing in mind, and as such, it provides a number of features and tools that make writing unit tests easier. One of these is the Angular CLI, which can be used to generate boilerplate unit test code.

There are also a number of third-party tools available that can be used to improve the efficiency and quality of your unit tests. Some of these tools include Karma, Jasmine, and Protractor.

Using the right tools for angular unit testing will make the process easier and help you write better tests.

4. Write tests for every component and service

If a component or service has no tests, it’s very likely that there are bugs in that code. By writing tests, you can be confident that your code is working as intended and that any bugs will be caught by the tests.

Not only that, but writing tests forces you to think about the functionality of your code and how it should work. This helps you write better code overall.

Finally, when you have a large codebase, it’s important to have tests in place so that you can refactor code with confidence. If a piece of code is covered by tests, you can be sure that changing it won’t break anything else in the codebase.

5. Make sure you mock dependencies

When you’re unit testing a component, you want to focus on that component only. You don’t want to be distracted by the behavior of its dependencies. If those dependencies change, your tests should still pass as long as the component’s behavior doesn’t change.

Mocking dependencies also allows you to test a component in isolation. This is especially important for components that rely on external services, like HTTP calls. By mocking the service, you can control its behavior and test different scenarios without having to make actual HTTP calls.

Last but not least, mocking dependencies makes your tests run faster because they don’t have to wait for the dependencies to finish executing.

6. Keep it simple

When tests are simple, they’re easier to write, understand, and maintain. They’re also less likely to break when the code changes.

This doesn’t mean that your tests should be trivial. They still need to cover all the important functionality of your code. But they should be as straightforward as possible.

One way to keep your tests simple is to avoid using too many helper functions. Helper functions can make your tests more difficult to understand and maintain. If you find yourself needing a lot of helper functions, it’s a good sign that your tests are too complex.

Another way to keep your tests simple is to avoid mocking too much. Mocking is a powerful tool, but it can make your tests harder to understand and maintain. Only mock what’s absolutely necessary.

Finally, keep your test suites small. A large test suite can be difficult to run and debug. It’s often better to split up a large test suite into smaller, more manageable pieces.

7. Avoid testing implementation details

When you’re testing a component, service, pipe, or directive, you should only be testing its public API. That means you should be testing how it’s used, not how it’s implemented.

For example, let’s say you have a component with a method that increments a counter. When you unit test this component, you should be testing that the counter is incremented when the method is called, not that the method is actually incrementing the counter.

The reason for this is that if you start testing implementation details, your tests will become brittle and will need to be updated every time you change the implementation. By contrast, if you focus on testing the public API, your tests will be more robust and won’t need to be changed nearly as often.

8. Test both positive and negative scenarios

If you only test the happy path, then you’re not really testing anything. All you’re doing is verifying that your code works when everything goes right. But what happens when something goes wrong? That’s where negative testing comes in.

Negative testing allows you to verify that your code handles errors and unexpected inputs gracefully. This is important because it helps ensure that your code is robust and can handle real-world conditions.

Positive and negative testing are both important, so be sure to include both in your angular unit tests.

9. Check that all inputs are valid

If an input is invalid, it can cause unexpected behavior in your application. This can lead to bugs that are difficult to track down and fix. By ensuring that all inputs are valid, you can avoid these problems.

There are two ways to do this. The first is to use the AngularJS built-in form validation. This will automatically check that all inputs are valid before the form is submitted.

The second way is to write a custom directive that checks the validity of an input. This is more work, but it gives you more control over how the input is validated.

Either way, checking that all inputs are valid is a crucial best practice in angular unit testing.

10. Test asynchronous code separately

When testing asynchronous code, there are two things that need to be considered: the state of the world before the async operation is executed, and the state of the world after the async operation is complete.

If you try to test both of these states in the same unit test, you will run into problems because the async operation may not have completed by the time the assertions are executed. This can lead to false positives (the async operation completes but the assertion fails) or false negatives (the async operation doesn’t complete but the assertion passes).

To avoid these problems, it’s best to split up your unit tests into two parts: one for testing the state of the world before the async operation is executed, and one for testing the state of the world after the async operation is complete.


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