Added UT for replica shard recovery

Signed-off-by: Ashish Singh <ssashish@amazon.com>

Author: ashking94

server/src/test/java/org/opensearch/index/shard/ReplicaRecoveryWithRemoteTranslogOnPrimaryTests.java

@@ -10,10 +10,15 @@
 
 import org.opensearch.cluster.metadata.IndexMetadata;
 import org.opensearch.common.settings.Settings;
+import org.opensearch.index.engine.DocIdSeqNoAndSource;
+import org.opensearch.index.engine.NRTReplicationEngine;
 import org.opensearch.index.engine.NRTReplicationEngineFactory;
 import org.opensearch.index.replication.OpenSearchIndexLevelReplicationTestCase;
+import org.opensearch.index.translog.WriteOnlyTranslogManager;
 import org.opensearch.indices.replication.common.ReplicationType;
 
+import java.util.List;
+
 public class ReplicaRecoveryWithRemoteTranslogOnPrimaryTests extends OpenSearchIndexLevelReplicationTestCase {
 
     private static final Settings settings = Settings.builder()
@@ -56,4 +61,35 @@ public void testReplicaShardRecoveryUptoLastFlushedCommit() throws Exception {
             shards.assertAllEqual(numDocs + moreDocs);
         }
     }
+
+    public void testNoTranslogHistoryTransferred() throws Exception {
+        try (ReplicationGroup shards = createGroup(0, settings, new NRTReplicationEngineFactory())) {
+
+            // Step1 - Start primary, index docs, flush, index more docs, check translog in primary as expected
+            shards.startPrimary();
+            final IndexShard primary = shards.getPrimary();
+            int numDocs = shards.indexDocs(randomIntBetween(10, 100));
+            shards.flush();
+            List<DocIdSeqNoAndSource> docIdAndSeqNosAfterFlush = getDocIdAndSeqNos(primary);
+            int moreDocs = shards.indexDocs(randomIntBetween(20, 100));
+            assertEquals(moreDocs, getTranslog(primary).totalOperations());
+
+            // Step 2 - Start replica, recovery happens, check docs recovered till last flush
+            final IndexShard replica = shards.addReplica();
+            shards.startAll();
+            assertEquals(docIdAndSeqNosAfterFlush, getDocIdAndSeqNos(replica));
+            assertDocCount(replica, numDocs);
+            assertEquals(NRTReplicationEngine.class, replica.getEngine().getClass());
+
+            // Step 3 - Check replica's translog has no operations
+            assertEquals(WriteOnlyTranslogManager.class, replica.getEngine().translogManager().getClass());
+            WriteOnlyTranslogManager replicaTranslogManager = (WriteOnlyTranslogManager) replica.getEngine().translogManager();
+            assertEquals(0, replicaTranslogManager.getTranslog().totalOperations());
+
+            // Adding this for close to succeed
+            shards.flush();
+            replicateSegments(primary, shards.getReplicas());
+            shards.assertAllEqual(numDocs + moreDocs);
+        }
+    }
 }