How to Successfully Unit Test Array Push in Angular with TypeScript

Learn how to effectively write unit tests for array operations in Angular and TypeScript, specifically focusing on array push methods and proper test coverage.
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Mastering Unit Tests for Array Push in Angular

Unit testing is a crucial part of software development, especially in frameworks like Angular and languages like TypeScript. It's essential not only for ensuring the reliability of your code but also for maintaining its quality over time. One common scenario faced by developers is testing array operations like push methods. In this post, we’ll tackle a specific question regarding unit testing an array push and how to effectively cover it in your tests.

The Problem at Hand

Imagine you have a component that loops through a set of values, checking for undefined entries and pushing defined values into an array. However, during your unit tests, you're facing a coverage issue with the array push line in your method. The method in question may look something like this:

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

In your unit tests, when attempting to check if the push operation has been called, you run into errors like "Cannot spyOn on a primitive value; undefined given”. Let’s break this down and find a solution.

Understanding the Solution

To effectively unit test this behavior, there are a few crucial steps to follow. Let’s go through them one at a time.

1. Correct the Conditional Check

In your original if statement, there is a logic flaw in checking for undefined values. Instead of using the string 'undefined', you should check against the undefined type itself. Here’s how to do that:

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

2. Define Content for Testing

To effectively test the behavior of showValues(), you need to provide it with content that simulates a realistic scenario. Here’s how you can set the content for your tests:

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

3. Call the Method and Assert the Results

Once the content is defined, you can call the showValues() method and check if the valueList array has actually been populated with the expected values. Your test could look like this:

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

4. Final Unit Test Example

Here is how your complete unit test would appear:

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

Conclusion

By correcting the condition for checking undefined values, defining suitable test content, and asserting the results effectively, you can ensure that your array push operations are thoroughly tested and covered in your unit tests. Mastering these techniques will not only improve the quality of your tests but also give you greater confidence in your code as you scale and enhance your Angular applications.

Happy testing!