Solving the setValidators of Null Error in Angular Unit Tests

Learn how to fix the `setValidators` of a null error while writing unit tests for Angular components that use FormGroups.
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This video is based on the question https://stackoverflow.com/q/65633628/ asked by the user 'Mrinal Chopra' ( https://stackoverflow.com/u/11027210/ ) and on the answer https://stackoverflow.com/a/65633882/ provided by the user 'jagjeet' ( https://stackoverflow.com/u/9274956/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the setValidators of Null Error in Angular

When writing unit tests in Angular, you might encounter various errors that can be frustrating and time-consuming to resolve. A common issue developers face is the TypeError: Cannot read property 'setValidators' of null during unit tests for components that utilize Angular’s FormGroup. This post will explain why this error occurs and how to successfully resolve it so that you can focus on what truly matters – writing effective and accurate tests.

The Problem Explained

The error message you typically see implies that you're trying to call the setValidators function on a reference that is null. This usually happens when you haven’t correctly initialized the controls in your FormGroup. Here’s a look at the relevant code snippets:

Component Code Overview

In the FormFieldInputV2Component, you're defining a FormGroup that presumably contains form controls. The ngOnInit lifecycle hook is utilized to set validators based on some configuration data:

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

The code attempts to access a control in the FormGroup using this.configData.name. If that specific control is not defined when the component is initialized, this.frmGroup.get(this.configData.name) will return null, leading to the error.

The Spec File Setup

In your test specifications, your initial setup for the FormGroup is as follows:

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

Assigning null to form controls is key to why you're encountering the error. When ngOnInit is executed, you're working with controls that have not been actually instantiated.

The Solution

To fix the mentioned issue, you'll need to ensure that the form controls are created properly in your test setup. Here’s how to do it effectively:

Step-by-Step Fix

Properly Initialize Form Controls:
Instead of assigning null, replace it with instances of FormControl. This guarantees that you have valid controls to work with when ngOnInit() runs.

Update your beforeEach block in the spec file as follows:

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

Test for Validator Functionality:
Ensure that you have appropriate tests to verify that the validators are functioning as intended. For example:

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

By making these adjustments, you will resolve the TypeError and ensure your tests run correctly.

Conclusion

In summary, the setValidators error commonly occurs when trying to access a control that hasn’t been properly initialized within the FormGroup. By ensuring that your form controls are instantiated with new FormControl(), you can avoid these frustrating issues and write robust, effective unit tests for your Angular components.

By following the steps outlined in this guide, you can easily fix this issue and improve your overall testing workflow for Angular applications. Happy coding!