Github user tzulitai commented on the issue:
https://github.com/apache/flink/pull/5181
Making the `AbstractFetcher::commitInternalOffsetsToKafka` non-final just
for the sake of testing using mocks really is not ideal.
I've opened a new PR #5189 that properly solves this by introducing a
proper abstraction for offset committing. Closing this PR in favor of the new
one.---
