How to Set Up NestJS Microservices Integration/E2E Testing with KafkaJS Consumer

Discover how to resolve issues with NestJS microservices integration testing for KafkaJS consumers. Learn essential steps to ensure message handling works seamlessly in your app.
---

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to set up NestJS microservices integration/e2e testing KafkaJS consumer (MessagePattern/EventPattern handler)

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Troubleshooting NestJS Microservices Integration Testing with KafkaJS Consumer

When working with NestJS and KafkaJS, setting up end-to-end (e2e) tests for microservices can sometimes be daunting. One common issue developers face is ensuring that the event listeners forKafkaJS consumers are configured to respond to emitted messages correctly. If you've found that your message handler isn't being invoked despite seemingly correct implementation, you're not alone! Let's explore the problem and its solution.

The Problem

A NestJS microservices setup using KafkaJS may result in an event listener that fails to trigger when a message is emitted. This was exactly the scenario faced by one developer, who reported that although their message was being emitted successfully, the corresponding handler function for the event was not being called.

Key Questions to Address:

Why is the event handler not being executed?

Are there any required waiting mechanisms for consumer events before messages can be processed?

Background Context

When using Kafka as a message broker, producers send messages to topics that consumers listen to. In this case, the developer had set up an event handler using the @ EventPattern() decorator, but it was not functioning as expected during their e2e tests. They were also unsure if they needed to wait for a specific consumer event (GROUP_JOIN) to complete before the handler could trigger.

Solution: Awaiting Message Consumption

The good news is this issue has a straightforward resolution. After thorough investigation, the developer discovered that for the handler to process the message correctly, it’s essential to introduce a wait time after emitting the message. This additional step allows the consumer handler the necessary time to catch and process the emitted message.

Here’s How to Implement the Solution:

Modify Your Message Emission:
After emitting a message, you need to ensure that your test properly awaits the response from the handler. This can be done by wrapping the emit function call in a promise.

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

Why setTimeout?
By awaiting a brief pause, it ensures that the microservice have enough time to process the emitted message before moving on in the test.

Validation:
After implementing the above change, rerun your tests. You should see logs from your consumer indicating that the message handler has successfully triggered and processed the message.

Conclusion

By adding a simple promise to await message consumption, NestJS microservices can effectively process KafkaJS messages during integration testing. Awaiting consumer events ensures that your application behaves as expected, making it easier to troubleshoot issues in the future.

Feel free to reach out if you have any further questions or need additional guidance on NestJS and KafkaJS integration testing! Happy coding!