Fixing https://github.com/mumrah/kafka-python/issues/434

Reworked the if statement logic to only call stop() on not-stopped objects.
added tests

kafka/producer/base.py

@@ -322,7 +322,7 @@ class Producer(object):
             self.thread.start()
 
             def cleanup(obj):
-                if obj.stopped:
+                if not obj.stopped:
                     obj.stop()
             self._cleanup_func = cleanup
             atexit.register(cleanup, self)

test/test_producer.py

@@ -91,6 +91,20 @@ class TestKafkaProducer(unittest.TestCase):
                     with self.assertRaises(FailedPayloadsError):
                         producer.send_messages('foobar', b'test message')
 
+    def test_cleanup_stop_is_called_on_not_stopped_object(self):
+        producer = Producer(MagicMock(), async=True)
+        producer.stopped = True
+        with patch('kafka.producer.base.Producer.stop') as base_stop:
+            producer._cleanup_func(producer)
+        self.assertEqual(base_stop.call_count, 0)
+
+    def test_cleanup_stop_is_not_called_on_stopped_object(self):
+        producer = Producer(MagicMock(), async=True)
+        producer.stopped = False
+        with patch('kafka.producer.base.Producer.stop') as base_stop:
+            producer._cleanup_func(producer)
+        self.assertEqual(base_stop.call_count, 1)
+
 
 class TestKafkaProducerSendUpstream(unittest.TestCase):