Possible Test Scenarios for a Kafka Consumer that Pushes Records to the S3 After Processing

I have a Kafka consumer that:

1. Consumes records from Kafka.
2. Processes each one of them in parallel by calling three down-stream services.
3. Pushes a final processed documents (corresponding to each record) into the S3.

Some additional info:

1. I am using commitAsync(..);

2. I am using Spring Reactor.

Apart from the happy case, what should be the possible scenarios that I should cover? Considering that I am processing an X amount of messages per poll(..) and processing and committing them all in parallel? I want my entire program to be tested as harshly as possible.