debug: add comprehensive consumer group tests and identify FindCoordinator issue

- Created consumer group tests for basic functionality, offset management, and rebalancing
- Added debug test to isolate consumer group coordination issues
- Root cause identified: Sarama repeatedly calls FindCoordinator but never progresses to JoinGroup
- Issue: Connections closed after FindCoordinator, preventing coordinator protocol
- Consumer group implementation exists but not being reached by Sarama clients

Next: Fix coordinator connection handling to enable JoinGroup protocol

test/kafka/consumer_group_debug_test.go

@@ -0,0 +1,154 @@
+package kafka
+
+import (
+	"context"
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/IBM/sarama"
+	"github.com/seaweedfs/seaweedfs/weed/mq/kafka/gateway"
+)
+
+func TestConsumerGroup_Debug(t *testing.T) {
+	// Start Kafka gateway
+	gatewayServer := gateway.NewServer(gateway.Options{Listen: ":0"})
+
+	go func() {
+		if err := gatewayServer.Start(); err != nil {
+			t.Logf("Gateway server error: %v", err)
+		}
+	}()
+	defer gatewayServer.Close()
+
+	// Wait for server to start
+	time.Sleep(100 * time.Millisecond)
+	host, port := gatewayServer.GetListenerAddr()
+	brokerAddr := fmt.Sprintf("%s:%d", host, port)
+
+	// Test configuration
+	topicName := "debug-test"
+	groupID := "debug-group"
+	
+	// Add topic for testing
+	gatewayServer.GetHandler().AddTopicForTesting(topicName, 1)
+
+	// Create Sarama config
+	config := sarama.NewConfig()
+	config.Version = sarama.V2_6_0_0
+	config.Consumer.Group.Rebalance.Strategy = sarama.BalanceStrategyRoundRobin
+	config.Consumer.Offsets.Initial = sarama.OffsetOldest
+	config.Consumer.Return.Errors = true
+	config.Producer.Return.Successes = true
+
+	// Produce one test message
+	t.Logf("=== Producing 1 test message ===")
+	producer, err := sarama.NewSyncProducer([]string{brokerAddr}, config)
+	if err != nil {
+		t.Fatalf("Failed to create producer: %v", err)
+	}
+	defer producer.Close()
+
+	message := &sarama.ProducerMessage{
+		Topic: topicName,
+		Key:   sarama.StringEncoder("debug-key"),
+		Value: sarama.StringEncoder("Debug Message"),
+	}
+
+	partition, offset, err := producer.SendMessage(message)
+	if err != nil {
+		t.Fatalf("Failed to produce message: %v", err)
+	}
+	t.Logf("✅ Produced message: partition=%d, offset=%d", partition, offset)
+
+	// Create a simple consumer group handler
+	handler := &DebugHandler{
+		messages: make(chan *sarama.ConsumerMessage, 1),
+		ready:    make(chan bool),
+		t:        t,
+	}
+
+	// Start one consumer
+	t.Logf("=== Starting 1 consumer in group '%s' ===", groupID)
+	
+	consumerGroup, err := sarama.NewConsumerGroup([]string{brokerAddr}, groupID, config)
+	if err != nil {
+		t.Fatalf("Failed to create consumer group: %v", err)
+	}
+	defer consumerGroup.Close()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	// Start consuming in a goroutine
+	go func() {
+		t.Logf("Starting consumption...")
+		err := consumerGroup.Consume(ctx, []string{topicName}, handler)
+		if err != nil && err != context.DeadlineExceeded {
+			t.Logf("Consumer error: %v", err)
+		}
+		t.Logf("Consumption finished")
+	}()
+
+	// Wait for consumer to be ready or timeout
+	t.Logf("Waiting for consumer to be ready...")
+	select {
+	case <-handler.ready:
+		t.Logf("✅ Consumer is ready!")
+		
+		// Try to consume the message
+		select {
+		case msg := <-handler.messages:
+			t.Logf("✅ Consumed message: key=%s, value=%s, offset=%d", 
+				string(msg.Key), string(msg.Value), msg.Offset)
+		case <-time.After(5 * time.Second):
+			t.Logf("⚠️ No message received within timeout")
+		}
+		
+	case <-time.After(8 * time.Second):
+		t.Logf("❌ Timeout waiting for consumer to be ready")
+	}
+
+	t.Logf("🎉 Debug test completed")
+}
+
+// DebugHandler implements sarama.ConsumerGroupHandler for debugging
+type DebugHandler struct {
+	messages chan *sarama.ConsumerMessage
+	ready    chan bool
+	t        *testing.T
+}
+
+func (h *DebugHandler) Setup(session sarama.ConsumerGroupSession) error {
+	h.t.Logf("🔧 Consumer group session setup - Generation: %d, Claims: %v", 
+		session.GenerationID(), session.Claims())
+	close(h.ready)
+	return nil
+}
+
+func (h *DebugHandler) Cleanup(session sarama.ConsumerGroupSession) error {
+	h.t.Logf("🧹 Consumer group session cleanup")
+	return nil
+}
+
+func (h *DebugHandler) ConsumeClaim(session sarama.ConsumerGroupSession, claim sarama.ConsumerGroupClaim) error {
+	h.t.Logf("🍽️ Starting to consume partition %d from offset %d", 
+		claim.Partition(), claim.InitialOffset())
+	
+	for {
+		select {
+		case message := <-claim.Messages():
+			if message == nil {
+				h.t.Logf("📭 Received nil message, ending consumption")
+				return nil
+			}
+			h.t.Logf("📨 Received message: key=%s, value=%s, offset=%d", 
+				string(message.Key), string(message.Value), message.Offset)
+			h.messages <- message
+			session.MarkMessage(message, "")
+		case <-session.Context().Done():
+			h.t.Logf("🛑 Session context done")
+			return nil
+		}
+	}
+}

test/kafka/consumer_group_test.go

@@ -0,0 +1,698 @@
+package kafka
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/IBM/sarama"
+	"github.com/seaweedfs/seaweedfs/weed/mq/kafka/gateway"
+)
+
+func TestConsumerGroup_BasicFunctionality(t *testing.T) {
+	// Start Kafka gateway
+	gatewayServer := gateway.NewServer(gateway.Options{Listen: ":0"})
+
+	go func() {
+		if err := gatewayServer.Start(); err != nil {
+			t.Logf("Gateway server error: %v", err)
+		}
+	}()
+	defer gatewayServer.Close()
+
+	// Wait for server to start
+	time.Sleep(100 * time.Millisecond)
+	host, port := gatewayServer.GetListenerAddr()
+	brokerAddr := fmt.Sprintf("%s:%d", host, port)
+
+	// Test configuration
+	topicName := "consumer-group-test"
+	
+	// Add topic for testing
+	gatewayServer.GetHandler().AddTopicForTesting(topicName, 1)
+	groupID := "test-consumer-group"
+	numConsumers := 3
+	numMessages := 9 // 3 messages per consumer
+
+	// Create Sarama config for consumer group
+	config := sarama.NewConfig()
+	config.Version = sarama.V2_6_0_0
+	config.Consumer.Group.Rebalance.Strategy = sarama.BalanceStrategyRoundRobin
+	config.Consumer.Offsets.Initial = sarama.OffsetOldest
+	config.Consumer.Return.Errors = true
+	config.Producer.Return.Successes = true
+
+	// Produce test messages first
+	t.Logf("=== Producing %d test messages ===", numMessages)
+	producer, err := sarama.NewSyncProducer([]string{brokerAddr}, config)
+	if err != nil {
+		t.Fatalf("Failed to create producer: %v", err)
+	}
+	defer producer.Close()
+
+	for i := 0; i < numMessages; i++ {
+		message := &sarama.ProducerMessage{
+			Topic: topicName,
+			Key:   sarama.StringEncoder(fmt.Sprintf("key-%d", i)),
+			Value: sarama.StringEncoder(fmt.Sprintf("Consumer Group Message %d", i+1)),
+		}
+
+		partition, offset, err := producer.SendMessage(message)
+		if err != nil {
+			t.Fatalf("Failed to produce message %d: %v", i, err)
+		}
+		t.Logf("✅ Produced message %d: partition=%d, offset=%d", i, partition, offset)
+	}
+
+	// Create consumer group handler
+	handler := &ConsumerGroupHandler{
+		messages: make(chan *sarama.ConsumerMessage, numMessages),
+		ready:    make(chan bool),
+		t:        t,
+	}
+
+	// Start multiple consumers in the same group
+	t.Logf("=== Starting %d consumers in group '%s' ===", numConsumers, groupID)
+	
+	var wg sync.WaitGroup
+	consumerErrors := make(chan error, numConsumers)
+	
+	for i := 0; i < numConsumers; i++ {
+		wg.Add(1)
+		go func(consumerID int) {
+			defer wg.Done()
+			
+			consumerGroup, err := sarama.NewConsumerGroup([]string{brokerAddr}, groupID, config)
+			if err != nil {
+				consumerErrors <- fmt.Errorf("consumer %d: failed to create consumer group: %v", consumerID, err)
+				return
+			}
+			defer consumerGroup.Close()
+
+			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+			defer cancel()
+
+			t.Logf("Consumer %d: Starting consumption", consumerID)
+			
+			// Start consuming
+			err = consumerGroup.Consume(ctx, []string{topicName}, handler)
+			if err != nil && err != context.DeadlineExceeded {
+				consumerErrors <- fmt.Errorf("consumer %d: consumption error: %v", consumerID, err)
+				return
+			}
+			
+			t.Logf("Consumer %d: Finished consumption", consumerID)
+		}(i)
+	}
+
+	// Wait for consumers to be ready
+	t.Logf("Waiting for consumers to be ready...")
+	readyCount := 0
+	for readyCount < numConsumers {
+		select {
+		case <-handler.ready:
+			readyCount++
+			t.Logf("Consumer ready: %d/%d", readyCount, numConsumers)
+		case <-time.After(5 * time.Second):
+			t.Fatalf("Timeout waiting for consumers to be ready")
+		}
+	}
+
+	// Collect consumed messages
+	t.Logf("=== Collecting consumed messages ===")
+	consumedMessages := make([]*sarama.ConsumerMessage, 0, numMessages)
+	messageTimeout := time.After(10 * time.Second)
+
+	for len(consumedMessages) < numMessages {
+		select {
+		case msg := <-handler.messages:
+			consumedMessages = append(consumedMessages, msg)
+			t.Logf("✅ Consumed message %d: key=%s, value=%s, partition=%d, offset=%d",
+				len(consumedMessages), string(msg.Key), string(msg.Value), msg.Partition, msg.Offset)
+		case err := <-consumerErrors:
+			t.Fatalf("Consumer error: %v", err)
+		case <-messageTimeout:
+			t.Fatalf("Timeout waiting for messages. Got %d/%d messages", len(consumedMessages), numMessages)
+		}
+	}
+
+	// Wait for all consumers to finish
+	wg.Wait()
+
+	// Verify all messages were consumed exactly once
+	if len(consumedMessages) != numMessages {
+		t.Errorf("Expected %d messages, got %d", numMessages, len(consumedMessages))
+	}
+
+	// Verify message uniqueness (no duplicates)
+	messageKeys := make(map[string]bool)
+	for _, msg := range consumedMessages {
+		key := string(msg.Key)
+		if messageKeys[key] {
+			t.Errorf("Duplicate message key: %s", key)
+		}
+		messageKeys[key] = true
+	}
+
+	// Verify all expected keys were received
+	for i := 0; i < numMessages; i++ {
+		expectedKey := fmt.Sprintf("key-%d", i)
+		if !messageKeys[expectedKey] {
+			t.Errorf("Missing message key: %s", expectedKey)
+		}
+	}
+
+	t.Logf("🎉 SUCCESS: Consumer group test completed with %d messages consumed by %d consumers", 
+		len(consumedMessages), numConsumers)
+}
+
+// ConsumerGroupHandler implements sarama.ConsumerGroupHandler
+type ConsumerGroupHandler struct {
+	messages chan *sarama.ConsumerMessage
+	ready    chan bool
+	t        *testing.T
+}
+
+func (h *ConsumerGroupHandler) Setup(sarama.ConsumerGroupSession) error {
+	h.t.Logf("Consumer group session setup")
+	close(h.ready)
+	return nil
+}
+
+func (h *ConsumerGroupHandler) Cleanup(sarama.ConsumerGroupSession) error {
+	h.t.Logf("Consumer group session cleanup")
+	return nil
+}
+
+func (h *ConsumerGroupHandler) ConsumeClaim(session sarama.ConsumerGroupSession, claim sarama.ConsumerGroupClaim) error {
+	for {
+		select {
+		case message := <-claim.Messages():
+			if message == nil {
+				return nil
+			}
+			h.messages <- message
+			session.MarkMessage(message, "")
+		case <-session.Context().Done():
+			return nil
+		}
+	}
+}
+
+func TestConsumerGroup_OffsetCommitAndFetch(t *testing.T) {
+	// Start Kafka gateway
+	gatewayServer := gateway.NewServer(gateway.Options{Listen: ":0"})
+
+	go func() {
+		if err := gatewayServer.Start(); err != nil {
+			t.Logf("Gateway server error: %v", err)
+		}
+	}()
+	defer gatewayServer.Close()
+
+	// Wait for server to start
+	time.Sleep(100 * time.Millisecond)
+	host, port := gatewayServer.GetListenerAddr()
+	brokerAddr := fmt.Sprintf("%s:%d", host, port)
+
+	// Test configuration
+	topicName := "offset-commit-test"
+	groupID := "offset-test-group"
+	numMessages := 5
+	
+	// Add topic for testing
+	gatewayServer.GetHandler().AddTopicForTesting(topicName, 1)
+
+	// Create Sarama config
+	config := sarama.NewConfig()
+	config.Version = sarama.V2_6_0_0
+	config.Consumer.Offsets.Initial = sarama.OffsetOldest
+	config.Consumer.Return.Errors = true
+	config.Producer.Return.Successes = true
+
+	// Produce test messages
+	t.Logf("=== Producing %d test messages ===", numMessages)
+	producer, err := sarama.NewSyncProducer([]string{brokerAddr}, config)
+	if err != nil {
+		t.Fatalf("Failed to create producer: %v", err)
+	}
+	defer producer.Close()
+
+	for i := 0; i < numMessages; i++ {
+		message := &sarama.ProducerMessage{
+			Topic: topicName,
+			Key:   sarama.StringEncoder(fmt.Sprintf("offset-key-%d", i)),
+			Value: sarama.StringEncoder(fmt.Sprintf("Offset Test Message %d", i+1)),
+		}
+
+		_, _, err := producer.SendMessage(message)
+		if err != nil {
+			t.Fatalf("Failed to produce message %d: %v", i, err)
+		}
+	}
+
+	// First consumer: consume first 3 messages and commit offsets
+	t.Logf("=== First consumer: consuming first 3 messages ===")
+	handler1 := &OffsetTestHandler{
+		messages:    make(chan *sarama.ConsumerMessage, numMessages),
+		ready:       make(chan bool),
+		stopAfter:   3,
+		t:           t,
+	}
+
+	consumerGroup1, err := sarama.NewConsumerGroup([]string{brokerAddr}, groupID, config)
+	if err != nil {
+		t.Fatalf("Failed to create first consumer group: %v", err)
+	}
+
+	ctx1, cancel1 := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel1()
+
+	// Start first consumer
+	go func() {
+		err := consumerGroup1.Consume(ctx1, []string{topicName}, handler1)
+		if err != nil && err != context.DeadlineExceeded {
+			t.Logf("First consumer error: %v", err)
+		}
+	}()
+
+	// Wait for first consumer to be ready
+	<-handler1.ready
+
+	// Collect messages from first consumer
+	consumedCount := 0
+	for consumedCount < 3 {
+		select {
+		case msg := <-handler1.messages:
+			consumedCount++
+			t.Logf("✅ First consumer message %d: key=%s, offset=%d", 
+				consumedCount, string(msg.Key), msg.Offset)
+		case <-time.After(5 * time.Second):
+			t.Fatalf("Timeout waiting for first consumer messages")
+		}
+	}
+
+	// Close first consumer (this should commit offsets)
+	consumerGroup1.Close()
+	cancel1()
+
+	// Wait a bit for cleanup
+	time.Sleep(500 * time.Millisecond)
+
+	// Second consumer: should start from offset 3 (after committed offset)
+	t.Logf("=== Second consumer: should resume from offset 3 ===")
+	handler2 := &OffsetTestHandler{
+		messages:    make(chan *sarama.ConsumerMessage, numMessages),
+		ready:       make(chan bool),
+		stopAfter:   2, // Should get remaining 2 messages
+		t:           t,
+	}
+
+	consumerGroup2, err := sarama.NewConsumerGroup([]string{brokerAddr}, groupID, config)
+	if err != nil {
+		t.Fatalf("Failed to create second consumer group: %v", err)
+	}
+	defer consumerGroup2.Close()
+
+	ctx2, cancel2 := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel2()
+
+	// Start second consumer
+	go func() {
+		err := consumerGroup2.Consume(ctx2, []string{topicName}, handler2)
+		if err != nil && err != context.DeadlineExceeded {
+			t.Logf("Second consumer error: %v", err)
+		}
+	}()
+
+	// Wait for second consumer to be ready
+	<-handler2.ready
+
+	// Collect messages from second consumer
+	secondConsumerMessages := make([]*sarama.ConsumerMessage, 0)
+	consumedCount = 0
+	for consumedCount < 2 {
+		select {
+		case msg := <-handler2.messages:
+			consumedCount++
+			secondConsumerMessages = append(secondConsumerMessages, msg)
+			t.Logf("✅ Second consumer message %d: key=%s, offset=%d", 
+				consumedCount, string(msg.Key), msg.Offset)
+		case <-time.After(5 * time.Second):
+			t.Fatalf("Timeout waiting for second consumer messages. Got %d/2", consumedCount)
+		}
+	}
+
+	// Verify second consumer started from correct offset
+	if len(secondConsumerMessages) > 0 {
+		firstMessageOffset := secondConsumerMessages[0].Offset
+		if firstMessageOffset < 3 {
+			t.Errorf("Expected second consumer to start from offset >= 3, got %d", firstMessageOffset)
+		} else {
+			t.Logf("✅ Second consumer correctly resumed from offset %d", firstMessageOffset)
+		}
+	}
+
+	t.Logf("🎉 SUCCESS: Offset commit/fetch test completed successfully")
+}
+
+// OffsetTestHandler implements sarama.ConsumerGroupHandler for offset testing
+type OffsetTestHandler struct {
+	messages  chan *sarama.ConsumerMessage
+	ready     chan bool
+	stopAfter int
+	consumed  int
+	t         *testing.T
+}
+
+func (h *OffsetTestHandler) Setup(sarama.ConsumerGroupSession) error {
+	h.t.Logf("Offset test consumer setup")
+	close(h.ready)
+	return nil
+}
+
+func (h *OffsetTestHandler) Cleanup(sarama.ConsumerGroupSession) error {
+	h.t.Logf("Offset test consumer cleanup")
+	return nil
+}
+
+func (h *OffsetTestHandler) ConsumeClaim(session sarama.ConsumerGroupSession, claim sarama.ConsumerGroupClaim) error {
+	for {
+		select {
+		case message := <-claim.Messages():
+			if message == nil {
+				return nil
+			}
+			h.consumed++
+			h.messages <- message
+			session.MarkMessage(message, "")
+			
+			// Stop after consuming the specified number of messages
+			if h.consumed >= h.stopAfter {
+				h.t.Logf("Stopping consumer after %d messages", h.consumed)
+				return nil
+			}
+		case <-session.Context().Done():
+			return nil
+		}
+	}
+}
+
+func TestConsumerGroup_Rebalancing(t *testing.T) {
+	// Start Kafka gateway
+	gatewayServer := gateway.NewServer(gateway.Options{Listen: ":0"})
+
+	go func() {
+		if err := gatewayServer.Start(); err != nil {
+			t.Logf("Gateway server error: %v", err)
+		}
+	}()
+	defer gatewayServer.Close()
+
+	// Wait for server to start
+	time.Sleep(100 * time.Millisecond)
+	host, port := gatewayServer.GetListenerAddr()
+	brokerAddr := fmt.Sprintf("%s:%d", host, port)
+
+	// Test configuration
+	topicName := "rebalance-test"
+	groupID := "rebalance-test-group"
+	numMessages := 12
+	
+	// Add topic for testing
+	gatewayServer.GetHandler().AddTopicForTesting(topicName, 1)
+
+	// Create Sarama config
+	config := sarama.NewConfig()
+	config.Version = sarama.V2_6_0_0
+	config.Consumer.Group.Rebalance.Strategy = sarama.BalanceStrategyRoundRobin
+	config.Consumer.Offsets.Initial = sarama.OffsetOldest
+	config.Consumer.Return.Errors = true
+	config.Consumer.Group.Session.Timeout = 10 * time.Second
+	config.Consumer.Group.Heartbeat.Interval = 3 * time.Second
+	config.Producer.Return.Successes = true
+
+	// Produce test messages
+	t.Logf("=== Producing %d test messages ===", numMessages)
+	producer, err := sarama.NewSyncProducer([]string{brokerAddr}, config)
+	if err != nil {
+		t.Fatalf("Failed to create producer: %v", err)
+	}
+	defer producer.Close()
+
+	for i := 0; i < numMessages; i++ {
+		message := &sarama.ProducerMessage{
+			Topic: topicName,
+			Key:   sarama.StringEncoder(fmt.Sprintf("rebalance-key-%d", i)),
+			Value: sarama.StringEncoder(fmt.Sprintf("Rebalance Test Message %d", i+1)),
+		}
+
+		_, _, err := producer.SendMessage(message)
+		if err != nil {
+			t.Fatalf("Failed to produce message %d: %v", i, err)
+		}
+	}
+
+	// Start with 2 consumers
+	t.Logf("=== Starting 2 initial consumers ===")
+	
+	handler1 := &RebalanceTestHandler{
+		messages:   make(chan *sarama.ConsumerMessage, numMessages),
+		ready:      make(chan bool),
+		rebalanced: make(chan bool, 5),
+		consumerID: "consumer-1",
+		t:          t,
+	}
+
+	handler2 := &RebalanceTestHandler{
+		messages:   make(chan *sarama.ConsumerMessage, numMessages),
+		ready:      make(chan bool),
+		rebalanced: make(chan bool, 5),
+		consumerID: "consumer-2",
+		t:          t,
+	}
+
+	// Start first consumer
+	consumerGroup1, err := sarama.NewConsumerGroup([]string{brokerAddr}, groupID, config)
+	if err != nil {
+		t.Fatalf("Failed to create consumer group 1: %v", err)
+	}
+	defer consumerGroup1.Close()
+
+	ctx1, cancel1 := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel1()
+
+	go func() {
+		err := consumerGroup1.Consume(ctx1, []string{topicName}, handler1)
+		if err != nil && err != context.DeadlineExceeded {
+			t.Logf("Consumer 1 error: %v", err)
+		}
+	}()
+
+	// Wait for first consumer to be ready
+	<-handler1.ready
+	t.Logf("Consumer 1 ready")
+
+	// Start second consumer
+	consumerGroup2, err := sarama.NewConsumerGroup([]string{brokerAddr}, groupID, config)
+	if err != nil {
+		t.Fatalf("Failed to create consumer group 2: %v", err)
+	}
+	defer consumerGroup2.Close()
+
+	ctx2, cancel2 := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel2()
+
+	go func() {
+		err := consumerGroup2.Consume(ctx2, []string{topicName}, handler2)
+		if err != nil && err != context.DeadlineExceeded {
+			t.Logf("Consumer 2 error: %v", err)
+		}
+	}()
+
+	// Wait for second consumer to be ready
+	<-handler2.ready
+	t.Logf("Consumer 2 ready")
+
+	// Wait for initial rebalancing
+	t.Logf("Waiting for initial rebalancing...")
+	rebalanceCount := 0
+	for rebalanceCount < 2 {
+		select {
+		case <-handler1.rebalanced:
+			rebalanceCount++
+			t.Logf("Consumer 1 rebalanced (%d/2)", rebalanceCount)
+		case <-handler2.rebalanced:
+			rebalanceCount++
+			t.Logf("Consumer 2 rebalanced (%d/2)", rebalanceCount)
+		case <-time.After(10 * time.Second):
+			t.Logf("Warning: Timeout waiting for initial rebalancing")
+			break
+		}
+	}
+
+	// Collect some messages
+	t.Logf("=== Collecting messages from 2 consumers ===")
+	allMessages := make([]*sarama.ConsumerMessage, 0)
+	messageTimeout := time.After(10 * time.Second)
+	
+	// Collect at least half the messages
+	for len(allMessages) < numMessages/2 {
+		select {
+		case msg := <-handler1.messages:
+			allMessages = append(allMessages, msg)
+			t.Logf("Consumer 1 message: key=%s, offset=%d", string(msg.Key), msg.Offset)
+		case msg := <-handler2.messages:
+			allMessages = append(allMessages, msg)
+			t.Logf("Consumer 2 message: key=%s, offset=%d", string(msg.Key), msg.Offset)
+		case <-messageTimeout:
+			break
+		}
+	}
+
+	t.Logf("Collected %d messages from 2 consumers", len(allMessages))
+
+	// Add a third consumer to trigger rebalancing
+	t.Logf("=== Adding third consumer to trigger rebalancing ===")
+	
+	handler3 := &RebalanceTestHandler{
+		messages:   make(chan *sarama.ConsumerMessage, numMessages),
+		ready:      make(chan bool),
+		rebalanced: make(chan bool, 5),
+		consumerID: "consumer-3",
+		t:          t,
+	}
+
+	consumerGroup3, err := sarama.NewConsumerGroup([]string{brokerAddr}, groupID, config)
+	if err != nil {
+		t.Fatalf("Failed to create consumer group 3: %v", err)
+	}
+	defer consumerGroup3.Close()
+
+	ctx3, cancel3 := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel3()
+
+	go func() {
+		err := consumerGroup3.Consume(ctx3, []string{topicName}, handler3)
+		if err != nil && err != context.DeadlineExceeded {
+			t.Logf("Consumer 3 error: %v", err)
+		}
+	}()
+
+	// Wait for third consumer to be ready
+	<-handler3.ready
+	t.Logf("Consumer 3 ready")
+
+	// Wait for rebalancing after adding third consumer
+	t.Logf("Waiting for rebalancing after adding third consumer...")
+	rebalanceCount = 0
+	rebalanceTimeout := time.After(15 * time.Second)
+	
+	for rebalanceCount < 3 {
+		select {
+		case <-handler1.rebalanced:
+			rebalanceCount++
+			t.Logf("Consumer 1 rebalanced after adding consumer 3 (%d/3)", rebalanceCount)
+		case <-handler2.rebalanced:
+			rebalanceCount++
+			t.Logf("Consumer 2 rebalanced after adding consumer 3 (%d/3)", rebalanceCount)
+		case <-handler3.rebalanced:
+			rebalanceCount++
+			t.Logf("Consumer 3 rebalanced (%d/3)", rebalanceCount)
+		case <-rebalanceTimeout:
+			t.Logf("Warning: Timeout waiting for rebalancing after adding consumer 3")
+			break
+		}
+	}
+
+	// Collect remaining messages from all 3 consumers
+	t.Logf("=== Collecting remaining messages from 3 consumers ===")
+	finalTimeout := time.After(10 * time.Second)
+	
+	for len(allMessages) < numMessages {
+		select {
+		case msg := <-handler1.messages:
+			allMessages = append(allMessages, msg)
+			t.Logf("Consumer 1 message: key=%s, offset=%d", string(msg.Key), msg.Offset)
+		case msg := <-handler2.messages:
+			allMessages = append(allMessages, msg)
+			t.Logf("Consumer 2 message: key=%s, offset=%d", string(msg.Key), msg.Offset)
+		case msg := <-handler3.messages:
+			allMessages = append(allMessages, msg)
+			t.Logf("Consumer 3 message: key=%s, offset=%d", string(msg.Key), msg.Offset)
+		case <-finalTimeout:
+			break
+		}
+	}
+
+	t.Logf("Final message count: %d/%d", len(allMessages), numMessages)
+
+	// Verify no duplicate messages
+	messageKeys := make(map[string]bool)
+	duplicates := 0
+	for _, msg := range allMessages {
+		key := string(msg.Key)
+		if messageKeys[key] {
+			duplicates++
+			t.Logf("Duplicate message key: %s", key)
+		}
+		messageKeys[key] = true
+	}
+
+	if duplicates > 0 {
+		t.Errorf("Found %d duplicate messages during rebalancing", duplicates)
+	}
+
+	t.Logf("🎉 SUCCESS: Rebalancing test completed. Consumed %d unique messages with %d consumers", 
+		len(messageKeys), 3)
+}
+
+// RebalanceTestHandler implements sarama.ConsumerGroupHandler for rebalancing tests
+type RebalanceTestHandler struct {
+	messages   chan *sarama.ConsumerMessage
+	ready      chan bool
+	rebalanced chan bool
+	consumerID string
+	t          *testing.T
+}
+
+func (h *RebalanceTestHandler) Setup(session sarama.ConsumerGroupSession) error {
+	h.t.Logf("%s: Setup - Generation: %d, Claims: %v", 
+		h.consumerID, session.GenerationID(), session.Claims())
+	
+	select {
+	case h.rebalanced <- true:
+	default:
+	}
+	
+	select {
+	case h.ready <- true:
+	default:
+	}
+	
+	return nil
+}
+
+func (h *RebalanceTestHandler) Cleanup(session sarama.ConsumerGroupSession) error {
+	h.t.Logf("%s: Cleanup", h.consumerID)
+	return nil
+}
+
+func (h *RebalanceTestHandler) ConsumeClaim(session sarama.ConsumerGroupSession, claim sarama.ConsumerGroupClaim) error {
+	h.t.Logf("%s: Starting to consume partition %d", h.consumerID, claim.Partition())
+	
+	for {
+		select {
+		case message := <-claim.Messages():
+			if message == nil {
+				return nil
+			}
+			h.messages <- message
+			session.MarkMessage(message, "")
+		case <-session.Context().Done():
+			return nil
+		}
+	}
+}