Do not fire MERGE events when merging MultiMap entries

Fixes hazelcast#13559

Multimap does not have MERGE listener anyway hence it's pointless
to fire MERGE events.

I also added additional parameters to the MultiMap split-brain test
to test every merge policy for both BINARY and OBJECT formats.

hazelcast/src/main/java/com/hazelcast/multimap/impl/operations/MergeOperation.java

@@ -16,7 +16,6 @@
 
 package com.hazelcast.multimap.impl.operations;
 
-import com.hazelcast.core.EntryEventType;
 import com.hazelcast.multimap.impl.MultiMapContainer;
 import com.hazelcast.multimap.impl.MultiMapDataSerializerHook;
 import com.hazelcast.multimap.impl.MultiMapMergeContainer;
@@ -75,7 +74,6 @@ public void run() throws Exception {
             MultiMapValue result = container.merge(mergeContainer, mergePolicy);
             if (result != null) {
                 resultMap.put(key, result.getCollection(false));
-                publishEvent(EntryEventType.MERGED, key, result, null);
             }
         }
         response = !resultMap.isEmpty();

hazelcast/src/test/java/com/hazelcast/multimap/MultiMapSplitBrainTest.java

@@ -19,7 +19,10 @@
 import com.hazelcast.config.Config;
 import com.hazelcast.config.MergePolicyConfig;
 import com.hazelcast.config.MultiMapConfig;
+import com.hazelcast.core.EntryEvent;
+import com.hazelcast.core.EntryListener;
 import com.hazelcast.core.HazelcastInstance;
+import com.hazelcast.core.MapEvent;
 import com.hazelcast.core.MultiMap;
 import com.hazelcast.spi.merge.DiscardMergePolicy;
 import com.hazelcast.spi.merge.HigherHitsMergePolicy;
@@ -70,13 +73,19 @@ public class MultiMapSplitBrainTest extends SplitBrainTestSupport {
     public static Collection<Object[]> parameters() {
         return asList(new Object[][]{
                 {DiscardMergePolicy.class, true},
+                {DiscardMergePolicy.class, false},
                 {HigherHitsMergePolicy.class, true},
+                {HigherHitsMergePolicy.class, false},
                 {LatestAccessMergePolicy.class, true},
+                {LatestAccessMergePolicy.class, false},
                 {LatestUpdateMergePolicy.class, true},
+                {LatestUpdateMergePolicy.class, false},
                 {PassThroughMergePolicy.class, true},
+                {PassThroughMergePolicy.class, false},
                 {PutIfAbsentMergePolicy.class, true},
+                {PutIfAbsentMergePolicy.class, false},
                 {RemoveValuesMergePolicy.class, true},
-
+                {RemoveValuesMergePolicy.class, false},
                 {ReturnPiCollectionMergePolicy.class, true},
                 {ReturnPiCollectionMergePolicy.class, false},
                 {MergeCollectionOfIntegerValuesMergePolicy.class, true},
@@ -133,6 +142,11 @@ protected void onAfterSplitBrainCreated(HazelcastInstance[] firstBrain, Hazelcas
         multiMapA2 = secondBrain[0].getMultiMap(multiMapNameA);
         multiMapB2 = secondBrain[0].getMultiMap(multiMapNameB);
 
+        EntryListener<Object, Object> listener = new EmptyEntryListener<Object, Object>();
+        multiMapA1.addEntryListener(listener, true);
+        multiMapA2.addEntryListener(listener, true);
+        multiMapB2.addEntryListener(listener, true);
+
         if (mergePolicyClass == DiscardMergePolicy.class) {
             afterSplitDiscardMergePolicy();
         } else if (mergePolicyClass == HigherHitsMergePolicy.class) {
@@ -458,4 +472,36 @@ private static void assertMultiMapsSize(MultiMap<?, ?> multiMap1, MultiMap<?, ?>
         }
         assertEqualsStringFormat("backupMultiMap should have size %d, but was %d", expectedSize, actualBackupSize);
     }
+
+    private static class EmptyEntryListener<K, V> implements EntryListener<K, V> {
+        @Override
+        public void mapEvicted(MapEvent event) {
+
+        }
+
+        @Override
+        public void mapCleared(MapEvent event) {
+
+        }
+
+        @Override
+        public void entryUpdated(EntryEvent<K, V> event) {
+
+        }
+
+        @Override
+        public void entryRemoved(EntryEvent<K, V> event) {
+
+        }
+
+        @Override
+        public void entryEvicted(EntryEvent<K, V> event) {
+
+        }
+
+        @Override
+        public void entryAdded(EntryEvent<K, V> event) {
+
+        }
+    }
 }