Fixed - RingBuffer#setCapacity, trim list incorrect

Signed-off-by: seakider <seakider@gmail.com>

redisson/src/main/java/org/redisson/RedissonRingBuffer.java

@@ -69,7 +69,9 @@ public class RedissonRingBuffer<V> extends RedissonQueue<V> implements RRingBuff
         return commandExecutor.evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_VOID,
                 "redis.call('set', KEYS[2], ARGV[1]); " +
                         "local len = redis.call('llen', KEYS[1]); " +
-                      "redis.call('ltrim', KEYS[1], len - tonumber(ARGV[1]), len - 1); ",
+                        "if len > tonumber(ARGV[1]) then " +
+                            "redis.call('ltrim', KEYS[1], len - tonumber(ARGV[1]), -1); " +
+                        "end; ",
              Arrays.asList(getRawName(), settingsName), capacity);
     }
 

redisson/src/test/java/org/redisson/RedissonRingBufferTest.java

@@ -31,6 +31,28 @@ public class RedissonRingBufferTest extends RedisDockerTest {
 
     }
 
+    @Test
+    public void testReSetCapacity() {
+        RRingBuffer<Integer> buffer = redisson.getRingBuffer("test");
+        buffer.trySetCapacity(3);
+        for (int i = 0; i < 3; i++) {
+            buffer.add(i);
+        }
+
+        assertThat(buffer).containsExactly(0, 1, 2);
+        assertThat(buffer.size()).isEqualTo(3);
+
+        // new capacity greater than list's length, not trim
+        buffer.setCapacity(5);
+        assertThat(buffer).containsExactly(0, 1, 2);
+        assertThat(buffer.size()).isEqualTo(3);
+
+        // new capacity less than list's length, trim size to new capacity
+        buffer.setCapacity(1);
+        assertThat(buffer).containsExactly(2);
+        assertThat(buffer.size()).isEqualTo(1);
+    }
+
     @Test
     public void testAdd() {
         RRingBuffer<Integer> buffer = redisson.getRingBuffer("test");