diff --git a/kombu/messaging.py b/kombu/messaging.py
index bac4e320..021abc13 100644
--- a/kombu/messaging.py
+++ b/kombu/messaging.py
@@ -68,9 +68,8 @@ class Producer(object):
         if auto_declare is not None:
             self.auto_declare = auto_declare
 
-        if self.exchange:
-            self.exchange = self.exchange(self.channel)
-            self.auto_declare and self.declare()
+        self.exchange = self.exchange(self.channel)
+        self.auto_declare and self.declare()
 
         if self.on_return:
             self.channel.events["basic_return"].append(self.on_return)
@@ -269,7 +268,12 @@ class Consumer(object):
 
     def cancel_by_queue(self, queue):
         """Cancel consumer by queue name."""
-        self.channel.basic_cancel(self._active_tags[queue])
+        try:
+            tag = self._active_tags.pop(queue)
+        except KeyError:
+            pass
+        else:
+            self.channel.basic_cancel(tag)
 
     def purge(self):
         """Purge messages from all queues.
diff --git a/kombu/tests/mocks.py b/kombu/tests/mocks.py
index 7cbf857e..d34ca473 100644
--- a/kombu/tests/mocks.py
+++ b/kombu/tests/mocks.py
@@ -25,6 +25,7 @@ class Channel(object):
         self.called = []
         self.deliveries = count(1).next
         self.to_deliver = []
+        self.events = {"basic_return": []}
 
     def _called(self, name):
         self.called.append(name)
@@ -73,7 +74,6 @@ class Channel(object):
             pass
 
     def queue_purge(self, *args, **kwargs):
-        print("PURGE!")
         self._called("queue_purge")
 
     def basic_consume(self, *args, **kwargs):
diff --git a/kombu/tests/test_messaging.py b/kombu/tests/test_messaging.py
index a90dc51b..020927ad 100644
--- a/kombu/tests/test_messaging.py
+++ b/kombu/tests/test_messaging.py
@@ -109,6 +109,23 @@ class test_Producer(unittest.TestCase):
         p = Producer(chan)
         self.assertFalse(p.exchange.name)
 
+    def test_revive(self):
+        chan = self.connection.channel()
+        p = Producer(chan)
+        chan2 = self.connection.channel()
+        p.revive(chan2)
+        self.assertIs(p.channel, chan2)
+        self.assertIs(p.exchange.channel, chan2)
+
+    def test_on_return(self):
+        chan = self.connection.channel()
+
+        def on_return(exception, exchange, routing_key, message):
+            pass
+
+        p = Producer(chan, on_return=on_return)
+        self.assertTrue(on_return in chan.events["basic_return"])
+
 
 class test_Consumer(unittest.TestCase):
 
@@ -138,6 +155,7 @@ class test_Consumer(unittest.TestCase):
         queue = Queue("qname", self.exchange, "rkey")
         consumer = Consumer(channel, queue, auto_declare=True)
         consumer.consume()
+        consumer.consume()  # twice is a noop
         self.assertIsNot(consumer.queues[0], queue)
         self.assertTrue(consumer.queues[0].is_bound)
         self.assertTrue(consumer.queues[0].exchange.is_bound)
@@ -151,6 +169,10 @@ class test_Consumer(unittest.TestCase):
         self.assertEqual(channel.called.count("basic_consume"), 1)
         self.assertTrue(consumer._active_tags)
 
+        consumer.cancel_by_queue(queue.name)
+        consumer.cancel_by_queue(queue.name)
+        self.assertFalse(consumer._active_tags)
+
     def test_manual_declare(self):
         channel = self.connection.channel()
         queue = Queue("qname", self.exchange, "rkey")
@@ -337,14 +359,13 @@ class test_Consumer(unittest.TestCase):
     def test_on_decode_error_callback(self):
         channel = self.connection.channel()
         b1 = Queue("qname1", self.exchange, "rkey")
-        consumer = Consumer(channel, [b1])
-        consumer.channel.throw_decode_error = True
         thrown = []
 
         def on_decode_error(msg, exc):
             thrown.append((msg.body, exc))
 
-        consumer.on_decode_error = on_decode_error
+        consumer = Consumer(channel, [b1], on_decode_error=on_decode_error)
+        consumer.channel.throw_decode_error = True
         consumer._receive_callback({"foo": "bar"})
 
         self.assertTrue(thrown)
@@ -358,3 +379,18 @@ class test_Consumer(unittest.TestCase):
         consumer = Consumer(channel, [b1])
         consumer.recover()
         self.assertIn("basic_recover", channel)
+
+    def test_revive(self):
+        channel = self.connection.channel()
+        b1 = Queue("qname1", self.exchange, "rkey")
+        consumer = Consumer(channel, [b1])
+        channel2 = self.connection.channel()
+        consumer.revive(channel2)
+        self.assertIs(consumer.channel, channel2)
+        self.assertIs(consumer.queues[0].channel, channel2)
+        self.assertIs(consumer.queues[0].exchange.channel, channel2)
+
+    def test__repr__(self):
+        channel = self.connection.channel()
+        b1 = Queue("qname1", self.exchange, "rkey")
+        self.assertTrue(repr(Consumer(channel, [b1])))
diff --git a/kombu/tests/test_virtual_scheduling.py b/kombu/tests/test_virtual_scheduling.py
index 20abbbde..bdeee651 100644
--- a/kombu/tests/test_virtual_scheduling.py
+++ b/kombu/tests/test_virtual_scheduling.py
@@ -48,3 +48,6 @@ class test_FairCycle(unittest.TestCase):
                          ("a", "a"), ("b", "b")])
         cycle2 = FairCycle(echo, ["c", "c"], MyEmpty)
         self.assertRaises(MyEmpty, consume, cycle2.get, 3)
+
+    def test__repr__(self):
+        self.assertTrue(repr(FairCycle(lambda x: x, [1, 2, 3], MyEmpty)))