How to Effectively Test a ParentComponent in EmberJS: Best Practices for Component Testing

Discover how to test components in EmberJS, focusing on the importance of testing the public API rather than implementation details.
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This video is based on the question https://stackoverflow.com/q/62885982/ asked by the user 'Andrew Zaw' ( https://stackoverflow.com/u/7601489/ ) and on the answer https://stackoverflow.com/a/62909062/ provided by the user 'jelhan' ( https://stackoverflow.com/u/3167221/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Effectively Test a ParentComponent in EmberJS: Best Practices for Component Testing

If you're venturing into the world of EmberJS, learning how to write meaningful tests for your components is crucial. One common challenge faced by newcomers is how to test a component that contains another component, like our example of a ParentComponent housing a ChildComponent. This guide will delve into the best practices for testing such scenarios in EmberJS and why focusing on the public API is essential.

The Challenge: Testing a Nested Component

Let's break down the situation. You've created a ParentComponent that includes a ChildComponent, and you want to ensure that a certain property, referred to as trait, is accurately set based on a boolean value defined within the ParentComponent. Here's a simplified structure of your ParentComponent:

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

In your test setup, you're attempting to validate that when someBoolean is true, the trait property passed to ChildComponent is also true. Initially, your test looks something like this:

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

Why This Approach is Not Ideal

While it may seem intuitive to check whether the ChildComponent receives the correct props, this testing method is generally discouraged in Ember's testing practices. Here's why:

Focus on Public API: Ember's testing framework is designed to ensure that the tests are centered around the public API of a component. That means it’s more beneficial to verify how the ParentComponent interacts with its environment rather than checking its internal workings.

Avoid Implementation Detail Testing: If you test nested components directly, you risk your tests becoming brittle. Refactoring a child component could break your tests even if the ParentComponent remains fully functional.

Recommended Approach: Testing the Outcome

Instead of verifying the internal state of the ChildComponent, you should focus on testing the output generated by the ParentComponent. By examining how this component renders under different conditions, you can effectively ensure that your application behaves as expected.

Steps to Test the Public API

Here are some steps you can follow to test the ParentComponent effectively:

Set Up the Test Environment: Start by rendering your ParentComponent with the necessary properties set appropriately.

Assert the Rendered Output: Instead of checking the ChildComponent, check the markup rendered by the ParentComponent itself. For example, if the trait impacts what is rendered, assert that those elements exist in the DOM.

Example Test Case:
Here's how an updated test case might look:

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

Conclusion

Learning to write tests in EmberJS may feel overwhelming at first, but by focusing on the public API and the results of your component's behavior, you'll create tests that are both robust and maintainable.

Always remember, testing the internal workings of components can lead to fragile testing setups, while validating the output renders the true functionality of your application. As you continue to learn EmberJS, keep these best practices in mind, and you'll be well on your way to mastering component testing!