@Test
    public void testCommitOffsetIllegalGeneration() {
        // we cannot retry if a rebalance occurs before the commit completed
        client.prepareResponse(groupCoordinatorResponse(node, Errors.NONE));
        coordinator.ensureCoordinatorReady(time.timer(Long.MAX_VALUE));

        prepareOffsetCommitRequest(singletonMap(t1p, 100L), Errors.ILLEGAL_GENERATION);
        assertThrows(CommitFailedException.class, () -> coordinator.commitOffsetsSync(singletonMap(t1p,
                new OffsetAndMetadata(100L, "metadata")), time.timer(Long.MAX_VALUE)));
    }
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