This library is used to mock a kafka server directly in Go for the purposes of unit testing. While it provides the ability to use a real kafka client against the mock server, it does not have nearly all of the capabilities of the official kafka server.
I find it is easier to maintain code this way, rather than place a facade in front of the kafka client and mock the client.
Install this dissector in Wireshark to examine the kafka protocol activity. You'll need to add port 21001 to its configuration. Analyze->Decode As->Add TCP port 21001 and decode as Kafka.