@Override
            public void onPartitionsRevoked(Collection<TopicPartition> partitions) {
                assertEquals(2, coordinator.groupMetadata().generationId());
            }
Verifies that subscription change updates SubscriptionState correctly even after JoinGroup failures
that don't re-invoke onJoinPrepare.
clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinatorTest.java