Have you encountered Kafka or RabbitMQ?

Yes, I have experience with Kafka and RabbitMQ.

Kafka is a distributed data streaming platform focused on high throughput and storing large volumes of messages. It is used for real-time event processing, logging, and system integration.

RabbitMQ is a message broker implementing the AMQP protocol, well-suited for managing message queues, load balancing, and ensuring guaranteed delivery.

In testing, it is important to verify message processing correctness, fault tolerance, delivery order, and performance. For example, you can write automated tests that publish messages and verify their receipt and processing by consumers, as well as simulate failures to test recovery.