Fixed - RBlockingQueue.drainTo doesn't work when queue contains only one element. #1809

redisson/src/main/java/org/redisson/RedissonBlockingQueue.java

@@ -150,7 +150,7 @@ public class RedissonBlockingQueue<V> extends RedissonQueue<V> implements RBlock
 
         return commandExecutor.evalWriteAsync(getName(), codec, new RedisCommand<Object>("EVAL", new ListDrainToDecoder(c)),
               "local vals = redis.call('lrange', KEYS[1], 0, -1); " +
-              "redis.call('ltrim', KEYS[1], -1, 0); " +
+              "redis.call('del', KEYS[1]); " +
               "return vals", Collections.<Object>singletonList(getName()));
     }
 

redisson/src/test/java/org/redisson/RedissonBlockingQueueTest.java

@@ -467,6 +467,18 @@ public class RedissonBlockingQueueTest extends RedissonQueueTest {
         assertThat(queue2).containsExactly(3, 4, 5, 6);
     }
 
+    @Test
+    public void testDrainToSingle() {
+        RBlockingQueue<Integer> queue = getQueue();
+        Assert.assertTrue(queue.add(1));
+        Assert.assertEquals(1, queue.size());
+        Set<Integer> batch = new HashSet<Integer>();
+        int count = queue.drainTo(batch);
+        Assert.assertEquals(1, count);
+        Assert.assertEquals(1, batch.size());
+        Assert.assertTrue(queue.isEmpty());
+    }
+    
     @Test
     public void testDrainTo() {
         RBlockingQueue<Integer> queue = getQueue();