We have seen how easy it is to write concise and readable component tests for Kafka producers in the last article. In this installment, we will focus on the read-side and write component tests for a Kafka consumer. The example is centered around the same small lifecycle event service that we saw in the last article.

Kafka for JUnit makes it easy to write integration tests for custom-built Kafka-enabled components as well as entire systems that integrate with a Kafka cluster. In the course of this article, I'd like to demonstrate how you can leverage this testing library to write whitebox tests for software components that integrate with Kafka. We'll start off with the write-path of a small lifecycle event service and implement a custom publisher on top of the Kafka Clients library that ought to be tested.