How to Test If an Array Contains Values from Another Array Using Jest

Learn how to effectively test if an array contains any values from another array using Jest, with simple examples and explanations.
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How to Test If an Array Contains Values from Another Array Using Jest

Testing can often be a daunting task, especially when it comes to checking arrays in JavaScript. If you're working with arrays and using Jest for your testing framework, you might find yourself asking: How can I check if an array contains any values from another array?

In this post, we'll discuss a practical solution to this problem. We’ll dive deep into how to test if any wild animal is listed in a domestic animal array.

The Problem Defined

You have two arrays:

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

You want to determine if any of the items in wildAnimals are present in domesticAnimals.

The Incorrect Approach

Initially, you might think that using the toContain method of Jest would suffice. Here’s an example attempt you made:

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

This approach fails because toContain is designed to check for a specific single value, not multiple values from another array.

The Solution

To effectively test whether there are any common values in both arrays, we can use the JavaScript method some() combined with includes().

Breaking Down the Solution

Using some():

This method tests whether at least one element in the array passes the condition implemented by the provided function.

Using includes():

This method checks if a particular value exists in the array.

So the correct way to formulate your test would be:

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

Explanation of the Code

Inside the test function:

If any of the domestic animals are also found in the wild animals array, the test will pass.

Important Note

In your original code, you marked the test functions as async, but since you're not using the await keyword anywhere, the async keyword is unnecessary.

Conclusion

By utilizing the combination of some() and includes(), you can check if there are any common values between two arrays in your Jest tests. This method is efficient and elegant, ensuring your code remains readable and maintainable.

Now you can confidently test array values in your JavaScript projects using Jest!