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Learn how to create a `JUnit 5 extension` that captures thread stack dumps when tests exceed the designated timeout, helping debug hangs quickly and effectively.
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How to Easily Dump All Thread Stacks on JUnit Timeout with a JUnit 5 Extension

If you are working with JUnit 5 and have encountered issues with tests hanging—particularly with cloud service drivers—you are not alone. It can be a frustrating experience, especially when the root cause isn't clear. A common approach to handle this situation is to configure JUnit to output stack traces of all threads when a timeout occurs.

In this guide, I'll guide you through creating a custom JUnit 5 extension that can effectively meet this requirement.

Why Use a JUnit 5 Extension?

Creating a custom JUnit extension allows you to implement specific behavior while running your tests without polluting your test code with additional boilerplate. This approach offers two main benefits:

Separation of Concerns: Your test methods remain clean and focused on their intended behavior.

Reusability: You can reuse the extension across different test classes.

Solution Overview

The solution involves two key components:

An extension class that implements the custom timeout logic.

An annotation that can be used to specify timeouts for your tests.

With these pieces in place, you can annotate your test classes to apply the timeout feature efficiently.

Step 1: Create the Timeout Annotation

Let's start by defining the @ Timeout annotation that will be used to specify the timeout duration for the tests.

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Step 2: Implement the Timeout Extension

Next, we will create the TimeoutExtension class. This class will handle the logic for enforcing the timeout and dumping thread states when timeouts occur.

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Step 3: Implement the Thread Dump Utility

We also need a utility class that can generate the thread dump when a timeout occurs.

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How to Use the Extension

To make use of the newly created extension:

Enable the extension on your test class.

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Simply annotate your test methods or test classes with @ Timeout providing the maximum execution time in seconds.

Conclusion

By implementing this JUnit 5 extension, you can gain insights into why tests hang and more effectively troubleshoot issues in your codebase. This approach allows for quick stack trace dumps of all threads when timeouts occur, significantly easing your debugging process.

Feel free to tweak the extension and utility classes to better match your specific project's requirements. Happy testing!