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Learn how to effectively test your login API using JEST for negative cases, ensuring your application handles invalid credentials correctly.
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This video is based on the question https://stackoverflow.com/q/62259386/ asked by the user 'Johnson Anthony' ( https://stackoverflow.com/u/7940365/ ) and on the answer https://stackoverflow.com/a/62259966/ provided by the user 'Łukasz Olszewski' ( https://stackoverflow.com/u/1151108/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Testing Your API: Handling Invalid Credentials in JEST

APIs form the backbone of modern applications, allowing different parts of the software to communicate effectively. However, ensuring your API handles errors gracefully is equally important as its success scenarios. When testing functionalities, especially login APIs, validating how the system reacts to invalid credentials is crucial for robust software performance. In this guide, we will explore how to set up negative API testing in JEST to ensure that our login API correctly responds with a 401 Unauthorized status code when invalid credentials are supplied.

The Problem: Testing Login API with Invalid Credentials

When you develop a login feature, it's not enough to only verify a successful login. You must also ensure that the system reacts appropriately when a user input invalid credentials. As the user stated, they encountered a validation issue while performing API tests with JEST. The test was designed to confirm that the API responded with a 401 status code when incorrect login details are used. The initial test implementation resulted in an error, highlighting the need for a more robust testing strategy.

Common Issue Encountered

In trying to validate the API test, the user received a misleading error message:

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

This message may suggest the test isn’t checking the API response properly, as it directly fails instead of letting you assert on the expected behavior.

The Solution: Testing for Negative Cases in JEST

To effectively test the login API with invalid credentials, you can modify your test case in one of two main ways. Let’s break down these solutions into clear sections.

Method 1: Using expect with toThrow

One straightforward approach is to assert that an error is thrown when sending a request with invalid credentials. Here’s how to implement this:

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Method 2: Try-Catch Block for Explicit Error Checking

Using a try-catch block allows you to handle the error explicitly. This can be particularly beneficial if you want to perform additional checks or log information when a failure occurs. The implementation would look like this:

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Summary of Solutions

Method 1: expect(...).toThrow – This is a concise way to assert that an error is thrown with the expected message.

Method 2: Using a try-catch block – This approach gives you more control and flexibility, allowing for additional assertions in case of error.

Conclusion

Testing the robustness of your API through negative testing is essential. Incorporating these techniques into your workflow will ensure that your application can gracefully handle invalid input. By verifying that your API returns a 401 Unauthorized status with invalid credentials, you can increase user trust and reliability in your software. Don't forget to regularly update your tests as you add new features to your application!

If you have any further questions or want to share your experiences with API testing in JEST, feel free to leave a comment below!