Скачать или смотреть Resolving the TypeError: expect(...).toBeInTheDocument is not a function in Jest Testing

This guide addresses a common issue when using Jest and Testing Library, specifically the `TypeError` encountered with `toBeInTheDocument`. Learn how to resolve this error and improve your React testing setup.
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Understanding the TypeError in Jest Testing

When working with Jest and React Testing Library, developers often rely on certain matchers to enhance their testing capabilities. However, encountering an error like TypeError: expect(...).toBeInTheDocument is not a function can be frustrating, especially when everything seems to be set up correctly. In this post, we'll dive into what this error means, why it occurs, and how to resolve it effectively.

What Causes the Error?

The crux of this issue lies in the setup configuration of your testing environment. Specifically, the toBeInTheDocument matcher is part of the @ testing-library/jest-dom library, which provides custom matchers for Jest tests. This error typically indicates that the matcher is not properly imported or extended in the configuration file.

Common Reasons for the Error:

Missing Import: The required matcher toBeInTheDocument is not imported correctly into your testing setup.

Incorrect Setup: The setup file may not be executed, or it might not be configured to include the necessary extensions properly.

Solving the Problem

To fix the TypeError, you just need a small modification to your setupTests.js file. Let’s go through the steps to clarify how you can implement this fix.

Step-by-Step Solution:

Locate Your Setup File: Open the src/setupTests.js file in your Create React App project. This file is the configuration point for Jest and extends its functionality for testing.

Import the Correct Matcher: Add the specific extension for the Jest DOM matchers at the top of your setupTests.js file. Your imports should look like this:

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

Save and Rerun Your Tests: After saving your changes, rerun your Jest tests. The error should no longer appear, and you should be able to use expect(...).toBeInTheDocument() without any issues.

Why This Works

By using the import statement import '@ testing-library/jest-dom/extend-expect';, you are extending Jest with additional matchers from jest-dom. This enhances your testing capabilities, allowing you to write more expressive test assertions like checking if an element is present in the document.

Conclusion

Encountering the TypeError: expect(...).toBeInTheDocument is not a function error can be disheartening, but with a simple adjustment to your testing setup, you can resolve it quickly. Remember to ensure all necessary imports are in place within your setupTests.js file to make the most out of the Jest and Testing Library experience.

By following this guide, you'll be well on your way to writing better tests for your React components, making your development process smoother and more efficient.