private void makeCoordinatorUnknown(ConsumerCoordinator coordinator, Errors error) {
        time.sleep(sessionTimeoutMs);
        coordinator.sendHeartbeatRequest();
        client.prepareResponse(heartbeatResponse(error));
        time.sleep(sessionTimeoutMs);
        consumerClient.poll(time.timer(0));
        assertTrue(coordinator.coordinatorUnknown());
    }
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