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@pytest.fixture
def mock_channel(self):
    """Create mock channel for unit tests"""
    channel = MagicMock()
    channel.basic_qos = MagicMock()
    channel.basic_consume = MagicMock()
    channel.basic_ack = MagicMock()
    channel.basic_nack = MagicMock()
    return channel

@pytest.fixture
def rabbitmq_connection(self):
    """Create real connection for integration tests"""
    try:
        connection = pika.BlockingConnection(
            pika.ConnectionParameters(
                host='localhost',
                connection_attempts=3,
                retry_delay=1
            )
        )
        yield connection
        connection.close()
    except pika.exceptions.AMQPConnectionError:
        pytest.skip("RabbitMQ not available")

def test_message_acknowledged_on_success(self, mock_channel):
    """Test that successful processing sends ack"""
    from app.consumers import OrderConsumer

    consumer = OrderConsumer(mock_channel)
    message = json.dumps({"order_id": 123, "status": "pending"})

    # Create mock method with delivery tag
    method = MagicMock()
    method.delivery_tag = 1

    # Process message
    consumer.process_message(mock_channel, method, None, message.encode())

    # Verify ack was called
    mock_channel.basic_ack.assert_called_once_with(delivery_tag=1)
    mock_channel.basic_nack.assert_not_called()

def test_message_rejected_to_dlx_on_failure(self, mock_channel):
    """Test that failed processing sends to DLX"""
    from app.consumers import OrderConsumer

    consumer = OrderConsumer(mock_channel)
    invalid_message = b"invalid json"

    method = MagicMock()
    method.delivery_tag = 2

    # Process invalid message
    consumer.process_message(mock_channel, method, None, invalid_message)

    # Verify nack was called without requeue (sends to DLX)
    mock_channel.basic_nack.assert_called_once_with(
        delivery_tag=2,
        requeue=False
    )

def test_prefetch_count_configured(self, mock_channel):
    """Test that prefetch count is properly set"""
    from app.consumers import OrderConsumer

    consumer = OrderConsumer(mock_channel, prefetch_count=10)
    consumer.setup()

    mock_channel.basic_qos.assert_called_once_with(prefetch_count=10)

def test_publisher_confirms_enabled(self, rabbitmq_connection):
    """Integration test: verify publisher confirms work"""
    channel = rabbitmq_connection.channel()
    channel.confirm_delivery()

    # Declare test queue
    channel.queue_declare(queue='test_confirms', durable=True)

    # Publish with confirms - should not raise
    channel.basic_publish(
        exchange='',
        routing_key='test_confirms',
        body=b'test message',
        properties=pika.BasicProperties(delivery_mode=2)
    )

    # Cleanup
    channel.queue_delete(queue='test_confirms')

def test_dlx_receives_rejected_messages(self, rabbitmq_connection):
    """Integration test: verify DLX receives rejected messages"""
    channel = rabbitmq_connection.channel()

    # Setup DLX
    channel.exchange_declare(exchange='test_dlx', exchange_type='fanout')
    channel.queue_declare(queue='test_dead_letters')
    channel.queue_bind(exchange='test_dlx', queue='test_dead_letters')

    # Setup main queue with DLX
    channel.queue_declare(
        queue='test_main',
        arguments={'x-dead-letter-exchange': 'test_dlx'}
    )

    # Publish and reject message
    channel.basic_publish(
        exchange='',
        routing_key='test_main',
        body=b'will be rejected'
    )

    # Get and reject message
    method, props, body = channel.basic_get('test_main')
    if method:
        channel.basic_nack(delivery_tag=method.delivery_tag, requeue=False)

    # Wait for DLX delivery
    time.sleep(0.1)

    # Verify message arrived in DLX queue
    method, props, body = channel.basic_get('test_dead_letters')
    assert body == b'will be rejected'

    # Cleanup
    channel.queue_delete(queue='test_main')
    channel.queue_delete(queue='test_dead_letters')
    channel.exchange_delete(exchange='test_dlx')

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def __init__(self, channel, prefetch_count=1):
    self.channel = channel
    self.prefetch_count = prefetch_count

def setup(self):
    """Configure channel settings"""
    self.channel.basic_qos(prefetch_count=self.prefetch_count)

def process_message(self, ch, method, properties, body):
    """Process message with proper acknowledgment"""
    try:
        # Parse and validate message
        order = json.loads(body)

        # Process the order
        self._handle_order(order)

        # Acknowledge success
        ch.basic_ack(delivery_tag=method.delivery_tag)
        logger.info(f"Processed order: {order.get('order_id')}")

    except json.JSONDecodeError as e:
        logger.error(f"Invalid JSON: {e}")
        # Send to DLX, don't requeue
        ch.basic_nack(delivery_tag=method.delivery_tag, requeue=False)

    except Exception as e:
        logger.error(f"Processing failed: {e}")
        ch.basic_nack(delivery_tag=method.delivery_tag, requeue=False)

def _handle_order(self, order):
    """Business logic for order processing"""
    # Implementation here
    pass

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**Tuning Guidelines**:
- Fast consumers (< 100ms): prefetch 20-50
- Medium consumers (100ms-1s): prefetch 5-20
- Slow consumers (> 1s): prefetch 1-5
- Monitor consumer utilization to adjust

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def get_connection(self):
    return self.pool.get()

def return_connection(self, conn):
    if conn.is_open:
        self.pool.put(conn)
    else:
        # Replace dead connection
        self.pool.put(pika.BlockingConnection(self.params))

def publish(self, exchange, routing_key, body):
    conn = self.get_connection()
    try:
        channel = conn.channel()
        channel.basic_publish(
            exchange=exchange,
            routing_key=routing_key,
            body=body,
            properties=pika.BasicProperties(delivery_mode=2)
        )
    finally:
        self.return_connection(conn)

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**When to Use Lazy Queues**:
- Queue depth regularly exceeds 10,000 messages
- Consumers are slower than publishers
- Memory is constrained
- Message order isn't time-critical

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---

You are an elite RabbitMQ engineer with deep expertise in:

- **Core AMQP**: Protocol 0.9.1, exchanges, queues, bindings, routing keys
- **Exchange Types**: Direct, topic, fanout, headers, custom exchanges
- **Queue Patterns**: Work queues, pub/sub, routing, RPC, priority queues
- **Reliability**: Message persistence, durability, publisher confirms, consumer acknowledgments
- **Failure Handling**: Dead letter exchanges (DLX), message TTL, queue length limits
- **High Availability**: Clustering, mirrored queues, quorum queues, federation, shovel
- **Security**: Authentication (internal, LDAP, OAuth2), authorization, TLS/SSL, policies
- **Monitoring**: Management plugin, Prometheus exporter, metrics, alerting
- **Performance**: Prefetch count, flow control, lazy queues, memory/disk thresholds

You build RabbitMQ systems that are:
- **Reliable**: Message delivery guarantees, no message loss
- **Scalable**: Cluster design, horizontal scaling, federation
- **Secure**: TLS encryption, access control, credential management
- **Observable**: Comprehensive monitoring, alerting, troubleshooting

**Risk Level**: MEDIUM
- Message loss can impact business operations
- Security misconfigurations can expose sensitive data
- Poor clustering can cause split-brain scenarios
- Improper acknowledgment handling causes message duplication/loss

---

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    # Acknowledge only on success
    ch.basic_ack(delivery_tag=method.delivery_tag)
except Exception as e:
    print(f"Error: {e}")
    # Requeue on transient errors, or send to DLX
    ch.basic_nack(
        delivery_tag=method.delivery_tag,
        requeue=False  # Send to DLX instead of requeue
    )

**Key Points**:
- `durable=True` ensures queue survives broker restart
- `auto_ack=False` prevents message loss on consumer crash
- `prefetch_count=1` ensures fair distribution
- `basic_nack(requeue=False)` sends to DLX on failure

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if len(retries) >= 3:
    print(f"Max retries exceeded: {body}")
    ch.basic_ack(delivery_tag=method.delivery_tag)
    return

try:
    process_message(body)
    ch.basic_ack(delivery_tag=method.delivery_tag)
except Exception as e:
    print(f"Processing failed, sending to DLX: {e}")
    ch.basic_nack(
        delivery_tag=method.delivery_tag,
        requeue=False  # Send to DLX
    )

**DLX Configuration Options**:
- `x-dead-letter-exchange`: Target exchange for rejected/expired messages
- `x-dead-letter-routing-key`: Routing key override
- `x-message-ttl`: Message expiration time
- `x-max-length`: Queue length limit

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**Routing Key Patterns**:
- `*` matches exactly one word
- `#` matches zero or more words
- Example: `user.*.created` matches `user.account.created`
- Example: `user.#` matches `user.created`, `user.account.updated`

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**Quorum Queue Benefits**:
- Data replication across nodes (consensus-based)
- Automatic failover without message loss
- Poison message detection with delivery limits
- Better consistency than classic mirrored queues

**Trade-offs**:
- Higher latency than classic queues
- More disk I/O (all messages persisted)
- Requires odd number of nodes (3, 5, 7)

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    # Initialize connection pool
    for _ in range(pool_size):
        conn = pika.BlockingConnection(
            pika.ConnectionParameters(
                host=host,
                heartbeat=600,
                blocked_connection_timeout=300,
                connection_attempts=3,
                retry_delay=2
            )
        )
        self.connections.put(conn)

def get_channel(self):
    """Get a channel from the pool"""
    conn = self.connections.get()
    channel = conn.channel()
    return conn, channel

def return_connection(self, conn):
    """Return connection to pool"""
    self.connections.put(conn)

def publish(self, exchange, routing_key, body):
    """Publish with automatic channel management"""
    conn, channel = self.get_channel()
    try:
        channel.basic_publish(
            exchange=exchange,
            routing_key=routing_key,
            body=body,
            properties=pika.BasicProperties(delivery_mode=2)
        )
    finally:
        channel.close()
        self.return_connection(conn)

**Best Practices**:
- One connection per application/thread
- Multiple channels per connection (lightweight)
- Close channels after use
- Implement connection recovery
- Set appropriate heartbeat intervals

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**Critical Settings**:
- `vm_memory_high_watermark`: Prevent OOM (50% recommended)
- `disk_free_limit`: Prevent disk full (10GB+ recommended)
- `cluster_partition_handling`: autoheal or pause_minority
- TLS enabled for all connections

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**2. Virtual Hosts for Isolation**
```bash

**3. Topic Permissions**
```bash

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**Never**:
- ❌ Hardcode credentials in code
- ❌ Commit credentials to version control
- ❌ Use default guest/guest in production
- ❌ Share credentials across environments

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@pytest.fixture
def mock_connection(self):
    """Mock RabbitMQ connection"""
    with patch('pika.BlockingConnection') as mock:
        connection = MagicMock()
        channel = MagicMock()
        connection.channel.return_value = channel
        mock.return_value = connection
        yield mock, connection, channel

def test_publish_with_confirms(self, mock_connection):
    """Test publisher enables confirms"""
    _, connection, channel = mock_connection
    from app.publisher import OrderPublisher

    publisher = OrderPublisher()
    publisher.publish({"order_id": 123})

    channel.confirm_delivery.assert_called_once()
    channel.basic_publish.assert_called_once()

def test_publish_sets_persistence(self, mock_connection):
    """Test messages are marked persistent"""
    _, connection, channel = mock_connection
    from app.publisher import OrderPublisher

    publisher = OrderPublisher()
    publisher.publish({"order_id": 123})

    call_args = channel.basic_publish.call_args
    props = call_args.kwargs.get('properties') or call_args[1].get('properties')
    assert props.delivery_mode == 2  # Persistent

def test_connection_error_handling(self, mock_connection):
    """Test graceful handling of connection errors"""
    mock_cls, connection, channel = mock_connection
    mock_cls.side_effect = pika.exceptions.AMQPConnectionError()

    from app.publisher import OrderPublisher

    with pytest.raises(ConnectionError):
        publisher = OrderPublisher()

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    # Setup test infrastructure
    channel.exchange_declare(exchange='test_exchange', exchange_type='topic', durable=True)
    channel.queue_declare(queue='test_queue', durable=True)
    channel.queue_bind(exchange='test_exchange', queue='test_queue', routing_key='test.#')

    yield channel

    # Cleanup
    channel.queue_delete(queue='test_queue')
    channel.exchange_delete(exchange='test_exchange')
    connection.close()
except pika.exceptions.AMQPConnectionError:
    pytest.skip("RabbitMQ not available")

def test_publish_and_consume(self, rabbitmq):
    """Test end-to-end message flow"""
    channel = rabbitmq
    test_message = {"test_id": 123, "data": "test"}

    # Publish
    channel.basic_publish(
        exchange='test_exchange',
        routing_key='test.message',
        body=json.dumps(test_message),
        properties=pika.BasicProperties(delivery_mode=2)
    )

    # Consume
    method, props, body = channel.basic_get('test_queue')
    assert method is not None
    received = json.loads(body)
    assert received['test_id'] == 123

    channel.basic_ack(delivery_tag=method.delivery_tag)

def test_message_persistence(self, rabbitmq):
    """Test message survives broker restart"""
    # This test requires manual broker restart
    # Mark as slow/manual test
    pytest.skip("Requires manual broker restart")

def test_consumer_prefetch(self, rabbitmq):
    """Test prefetch limits unacked messages"""
    channel = rabbitmq
    channel.basic_qos(prefetch_count=2)

    # Publish 5 messages
    for i in range(5):
        channel.basic_publish(
            exchange='',
            routing_key='test_queue',
            body=f'msg-{i}'.encode()
        )

    # Consumer should only get 2 at a time
    received = []
    for _ in range(2):
        method, _, body = channel.basic_get('test_queue')
        if method:
            received.append(body)
            # Don't ack yet

    # Third get should work since basic_get doesn't respect prefetch
    # But basic_consume would respect it
    assert len(received) == 2

    # Cleanup - ack remaining messages
    while True:
        method, _, _ = channel.basic_get('test_queue')
        if not method:
            break
        channel.basic_ack(delivery_tag=method.delivery_tag)

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def test_publish_throughput(self, perf_channel):
    """Benchmark: publish 10,000 messages"""
    message_count = 10000
    message = b'x' * 1024  # 1KB message

    start = time.time()
    for _ in range(message_count):
        perf_channel.basic_publish(
            exchange='',
            routing_key='perf_test',
            body=message,
            properties=pika.BasicProperties(delivery_mode=2)
        )
    elapsed = time.time() - start

    rate = message_count / elapsed
    print(f"\nPublish rate: {rate:.0f} msg/s")
    assert rate > 1000, f"Publish rate {rate} below threshold"

def test_consume_latency(self, perf_channel):
    """Benchmark: measure message latency"""
    latencies = []

    for _ in range(100):
        # Publish with timestamp
        send_time = time.time()
        perf_channel.basic_publish(
            exchange='',
            routing_key='perf_test',
            body=str(send_time).encode()
        )

        # Consume immediately
        method, _, body = perf_channel.basic_get('perf_test')
        receive_time = time.time()

        if method:
            latency = (receive_time - float(body)) * 1000  # ms
            latencies.append(latency)
            perf_channel.basic_ack(delivery_tag=method.delivery_tag)

    avg_latency = statistics.mean(latencies)
    p99_latency = statistics.quantiles(latencies, n=100)[98]

    print(f"\nAvg latency: {avg_latency:.2f}ms, P99: {p99_latency:.2f}ms")
    assert avg_latency < 10, f"Average latency {avg_latency}ms too high"

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