Remove use of {String,UUID}Identifier
[controller.git] / opendaylight / md-sal / sal-akka-raft / src / test / java / org / opendaylight / controller / cluster / raft / behaviors / LeaderTest.java
index c57fce1cd553d8c41dd786d9c4bb6f33e97791b6..1caf631cee883c8ed40d8bc15eca1392c69bac85 100644 (file)
@@ -1,36 +1,54 @@
+/*
+ * Copyright (c) 2014, 2015 Cisco Systems, Inc. and others.  All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ */
+
 package org.opendaylight.controller.cluster.raft.behaviors;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
 import akka.actor.ActorRef;
 import akka.actor.PoisonPill;
 import akka.actor.Props;
 import akka.actor.Terminated;
 import akka.testkit.JavaTestKit;
 import akka.testkit.TestActorRef;
-import com.google.common.base.Optional;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.util.concurrent.Uninterruptibles;
 import com.google.protobuf.ByteString;
+import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 import org.junit.After;
-import org.junit.Assert;
 import org.junit.Test;
 import org.opendaylight.controller.cluster.raft.DefaultConfigParamsImpl;
 import org.opendaylight.controller.cluster.raft.FollowerLogInformation;
 import org.opendaylight.controller.cluster.raft.MockRaftActorContext;
 import org.opendaylight.controller.cluster.raft.RaftActorContext;
+import org.opendaylight.controller.cluster.raft.RaftActorLeadershipTransferCohort;
 import org.opendaylight.controller.cluster.raft.RaftState;
+import org.opendaylight.controller.cluster.raft.RaftVersions;
+import org.opendaylight.controller.cluster.raft.ReplicatedLogEntry;
 import org.opendaylight.controller.cluster.raft.ReplicatedLogImplEntry;
 import org.opendaylight.controller.cluster.raft.SerializationUtils;
-import org.opendaylight.controller.cluster.raft.base.messages.ApplyLogEntries;
+import org.opendaylight.controller.cluster.raft.Snapshot;
+import org.opendaylight.controller.cluster.raft.VotingState;
+import org.opendaylight.controller.cluster.raft.base.messages.ApplyJournalEntries;
 import org.opendaylight.controller.cluster.raft.base.messages.ApplyState;
 import org.opendaylight.controller.cluster.raft.base.messages.CaptureSnapshot;
-import org.opendaylight.controller.cluster.raft.base.messages.IsolatedLeaderCheck;
+import org.opendaylight.controller.cluster.raft.base.messages.ElectionTimeout;
 import org.opendaylight.controller.cluster.raft.base.messages.Replicate;
 import org.opendaylight.controller.cluster.raft.base.messages.SendHeartBeat;
 import org.opendaylight.controller.cluster.raft.base.messages.SendInstallSnapshot;
@@ -41,14 +59,17 @@ import org.opendaylight.controller.cluster.raft.messages.InstallSnapshot;
 import org.opendaylight.controller.cluster.raft.messages.InstallSnapshotReply;
 import org.opendaylight.controller.cluster.raft.messages.RaftRPC;
 import org.opendaylight.controller.cluster.raft.messages.RequestVoteReply;
+import org.opendaylight.controller.cluster.raft.policy.DefaultRaftPolicy;
+import org.opendaylight.controller.cluster.raft.policy.RaftPolicy;
 import org.opendaylight.controller.cluster.raft.utils.ForwardMessageToBehaviorActor;
 import org.opendaylight.controller.cluster.raft.utils.MessageCollectorActor;
-import org.opendaylight.controller.protobuff.messages.cluster.raft.InstallSnapshotMessages;
+import org.opendaylight.yangtools.concepts.Identifier;
 import scala.concurrent.duration.FiniteDuration;
 
-public class LeaderTest extends AbstractLeaderTest {
+public class LeaderTest extends AbstractLeaderTest<Leader> {
 
     static final String FOLLOWER_ID = "follower";
+    public static final String LEADER_ID = "leader";
 
     private final TestActorRef<ForwardMessageToBehaviorActor> leaderActor = actorFactory.createTestActor(
             Props.create(ForwardMessageToBehaviorActor.class), actorFactory.generateActorId("leader"));
@@ -57,6 +78,7 @@ public class LeaderTest extends AbstractLeaderTest {
             Props.create(ForwardMessageToBehaviorActor.class), actorFactory.generateActorId("follower"));
 
     private Leader leader;
+    private final short payloadVersion = 5;
 
     @Override
     @After
@@ -74,10 +96,8 @@ public class LeaderTest extends AbstractLeaderTest {
 
         leader = new Leader(createActorContext());
 
-        // handle message should return the Leader state when it receives an
-        // unknown message
-        RaftActorBehavior behavior = leader.handleMessage(followerActor, "foo");
-        Assert.assertTrue(behavior instanceof Leader);
+        // handle message should null when it receives an unknown message
+        assertNull(leader.handleMessage(followerActor, "foo"));
     }
 
     @Test
@@ -85,11 +105,14 @@ public class LeaderTest extends AbstractLeaderTest {
         logStart("testThatLeaderSendsAHeartbeatMessageToAllFollowers");
 
         MockRaftActorContext actorContext = createActorContextWithFollower();
+        short payloadVersion = (short)5;
+        actorContext.setPayloadVersion(payloadVersion);
 
         long term = 1;
         actorContext.getTermInformation().update(term, "");
 
         leader = new Leader(actorContext);
+        actorContext.setCurrentBehavior(leader);
 
         // Leader should send an immediate heartbeat with no entries as follower is inactive.
         long lastIndex = actorContext.getReplicatedLog().lastIndex();
@@ -98,10 +121,11 @@ public class LeaderTest extends AbstractLeaderTest {
         assertEquals("getPrevLogIndex", -1, appendEntries.getPrevLogIndex());
         assertEquals("getPrevLogTerm", -1, appendEntries.getPrevLogTerm());
         assertEquals("Entries size", 0, appendEntries.getEntries().size());
+        assertEquals("getPayloadVersion", payloadVersion, appendEntries.getPayloadVersion());
 
         // The follower would normally reply - simulate that explicitly here.
         leader.handleMessage(followerActor, new AppendEntriesReply(
-                FOLLOWER_ID, term, true, lastIndex - 1, term));
+                FOLLOWER_ID, term, true, lastIndex - 1, term, (short)0));
         assertEquals("isFollowerActive", true, leader.getFollower(FOLLOWER_ID).isFollowerActive());
 
         followerActor.underlyingActor().clear();
@@ -110,7 +134,7 @@ public class LeaderTest extends AbstractLeaderTest {
         Uninterruptibles.sleepUninterruptibly(actorContext.getConfigParams().
                 getHeartBeatInterval().toMillis(), TimeUnit.MILLISECONDS);
 
-        leader.handleMessage(leaderActor, new SendHeartBeat());
+        leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
 
         appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
         assertEquals("getPrevLogIndex", lastIndex - 1, appendEntries.getPrevLogIndex());
@@ -118,6 +142,20 @@ public class LeaderTest extends AbstractLeaderTest {
         assertEquals("Entries size", 1, appendEntries.getEntries().size());
         assertEquals("Entry getIndex", lastIndex, appendEntries.getEntries().get(0).getIndex());
         assertEquals("Entry getTerm", term, appendEntries.getEntries().get(0).getTerm());
+        assertEquals("getPayloadVersion", payloadVersion, appendEntries.getPayloadVersion());
+    }
+
+
+    private RaftActorBehavior sendReplicate(MockRaftActorContext actorContext, long index){
+        return sendReplicate(actorContext, 1, index);
+    }
+
+    private RaftActorBehavior sendReplicate(MockRaftActorContext actorContext, long term, long index){
+        MockRaftActorContext.MockPayload payload = new MockRaftActorContext.MockPayload("foo");
+        MockRaftActorContext.MockReplicatedLogEntry newEntry = new MockRaftActorContext.MockReplicatedLogEntry(
+                term, index, payload);
+        actorContext.getReplicatedLog().append(newEntry);
+        return leader.handleMessage(leaderActor, new Replicate(null, null, newEntry));
     }
 
     @Test
@@ -137,17 +175,103 @@ public class LeaderTest extends AbstractLeaderTest {
         // The follower would normally reply - simulate that explicitly here.
         long lastIndex = actorContext.getReplicatedLog().lastIndex();
         leader.handleMessage(followerActor, new AppendEntriesReply(
-                FOLLOWER_ID, term, true, lastIndex, term));
+                FOLLOWER_ID, term, true, lastIndex, term, (short)0));
         assertEquals("isFollowerActive", true, leader.getFollower(FOLLOWER_ID).isFollowerActive());
 
         followerActor.underlyingActor().clear();
 
-        MockRaftActorContext.MockPayload payload = new MockRaftActorContext.MockPayload("foo");
-        MockRaftActorContext.MockReplicatedLogEntry newEntry = new MockRaftActorContext.MockReplicatedLogEntry(
-                1, lastIndex + 1, payload);
-        actorContext.getReplicatedLog().append(newEntry);
-        RaftActorBehavior raftBehavior = leader.handleMessage(leaderActor,
-                new Replicate(null, null, newEntry));
+        RaftActorBehavior raftBehavior = sendReplicate(actorContext, lastIndex + 1);
+
+        // State should not change
+        assertTrue(raftBehavior instanceof Leader);
+
+        AppendEntries appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        assertEquals("getPrevLogIndex", lastIndex, appendEntries.getPrevLogIndex());
+        assertEquals("getPrevLogTerm", term, appendEntries.getPrevLogTerm());
+        assertEquals("Entries size", 1, appendEntries.getEntries().size());
+        assertEquals("Entry getIndex", lastIndex + 1, appendEntries.getEntries().get(0).getIndex());
+        assertEquals("Entry getTerm", term, appendEntries.getEntries().get(0).getTerm());
+        assertEquals("Entry payload", "foo", appendEntries.getEntries().get(0).getData().toString());
+        assertEquals("Commit Index", lastIndex, actorContext.getCommitIndex());
+    }
+
+    @Test
+    public void testHandleReplicateMessageWithHigherTermThanPreviousEntry() throws Exception {
+        logStart("testHandleReplicateMessageWithHigherTermThanPreviousEntry");
+
+        MockRaftActorContext actorContext = createActorContextWithFollower();
+
+        // The raft context is initialized with a couple log entries. However the commitIndex
+        // is -1, simulating that the leader previously didn't get consensus and thus the log entries weren't
+        // committed and applied. Now it regains leadership with a higher term (2).
+        long prevTerm = actorContext.getTermInformation().getCurrentTerm();
+        long newTerm = prevTerm + 1;
+        actorContext.getTermInformation().update(newTerm, "");
+
+        leader = new Leader(actorContext);
+        actorContext.setCurrentBehavior(leader);
+
+        // Leader will send an immediate heartbeat - ignore it.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        // The follower replies with the leader's current last index and term, simulating that it is
+        // up to date with the leader.
+        long lastIndex = actorContext.getReplicatedLog().lastIndex();
+        leader.handleMessage(followerActor, new AppendEntriesReply(
+                FOLLOWER_ID, newTerm, true, lastIndex, prevTerm, (short)0));
+
+        // The commit index should not get updated even though consensus was reached. This is b/c the
+        // last entry's term does match the current term. As per §5.4.1, "Raft never commits log entries
+        // from previous terms by counting replicas".
+        assertEquals("Commit Index", -1, actorContext.getCommitIndex());
+
+        followerActor.underlyingActor().clear();
+
+        // Now replicate a new entry with the new term 2.
+        long newIndex = lastIndex + 1;
+        sendReplicate(actorContext, newTerm, newIndex);
+
+        AppendEntries appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        assertEquals("getPrevLogIndex", lastIndex, appendEntries.getPrevLogIndex());
+        assertEquals("getPrevLogTerm", prevTerm, appendEntries.getPrevLogTerm());
+        assertEquals("Entries size", 1, appendEntries.getEntries().size());
+        assertEquals("Entry getIndex", newIndex, appendEntries.getEntries().get(0).getIndex());
+        assertEquals("Entry getTerm", newTerm, appendEntries.getEntries().get(0).getTerm());
+        assertEquals("Entry payload", "foo", appendEntries.getEntries().get(0).getData().toString());
+
+        // The follower replies with success. The leader should now update the commit index to the new index
+        // as per §5.4.1 "once an entry from the current term is committed by counting replicas, then all
+        // prior entries are committed indirectly".
+        leader.handleMessage(followerActor, new AppendEntriesReply(
+                FOLLOWER_ID, newTerm, true, newIndex, newTerm, (short)0));
+
+        assertEquals("Commit Index", newIndex, actorContext.getCommitIndex());
+    }
+
+    @Test
+    public void testHandleReplicateMessageCommitIndexIncrementedBeforeConsensus() throws Exception {
+        logStart("testHandleReplicateMessageCommitIndexIncrementedBeforeConsensus");
+
+        MockRaftActorContext actorContext = createActorContextWithFollower();
+        actorContext.setRaftPolicy(createRaftPolicy(true, true));
+
+        long term = 1;
+        actorContext.getTermInformation().update(term, "");
+
+        leader = new Leader(actorContext);
+
+        // Leader will send an immediate heartbeat - ignore it.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        // The follower would normally reply - simulate that explicitly here.
+        long lastIndex = actorContext.getReplicatedLog().lastIndex();
+        leader.handleMessage(followerActor, new AppendEntriesReply(
+                FOLLOWER_ID, term, true, lastIndex, term, (short) 0));
+        assertEquals("isFollowerActive", true, leader.getFollower(FOLLOWER_ID).isFollowerActive());
+
+        followerActor.underlyingActor().clear();
+
+        RaftActorBehavior raftBehavior = sendReplicate(actorContext, lastIndex + 1);
 
         // State should not change
         assertTrue(raftBehavior instanceof Leader);
@@ -158,9 +282,222 @@ public class LeaderTest extends AbstractLeaderTest {
         assertEquals("Entries size", 1, appendEntries.getEntries().size());
         assertEquals("Entry getIndex", lastIndex + 1, appendEntries.getEntries().get(0).getIndex());
         assertEquals("Entry getTerm", term, appendEntries.getEntries().get(0).getTerm());
-        assertEquals("Entry payload", payload, appendEntries.getEntries().get(0).getData());
+        assertEquals("Entry payload", "foo", appendEntries.getEntries().get(0).getData().toString());
+        assertEquals("Commit Index", lastIndex+1, actorContext.getCommitIndex());
+    }
+
+    @Test
+    public void testMultipleReplicateShouldNotCauseDuplicateAppendEntriesToBeSent() throws Exception {
+        logStart("testHandleReplicateMessageSendAppendEntriesToFollower");
+
+        MockRaftActorContext actorContext = createActorContextWithFollower();
+        actorContext.setConfigParams(new DefaultConfigParamsImpl() {
+            @Override
+            public FiniteDuration getHeartBeatInterval() {
+                return FiniteDuration.apply(5, TimeUnit.SECONDS);
+            }
+        });
+
+        long term = 1;
+        actorContext.getTermInformation().update(term, "");
+
+        leader = new Leader(actorContext);
+
+        // Leader will send an immediate heartbeat - ignore it.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        // The follower would normally reply - simulate that explicitly here.
+        long lastIndex = actorContext.getReplicatedLog().lastIndex();
+        leader.handleMessage(followerActor, new AppendEntriesReply(
+                FOLLOWER_ID, term, true, lastIndex, term, (short)0));
+        assertEquals("isFollowerActive", true, leader.getFollower(FOLLOWER_ID).isFollowerActive());
+
+        followerActor.underlyingActor().clear();
+
+        for(int i=0;i<5;i++) {
+            sendReplicate(actorContext, lastIndex+i+1);
+        }
+
+        List<AppendEntries> allMessages = MessageCollectorActor.getAllMatching(followerActor, AppendEntries.class);
+        // We expect only 1 message to be sent because of two reasons,
+        // - an append entries reply was not received
+        // - the heartbeat interval has not expired
+        // In this scenario if multiple messages are sent they would likely be duplicates
+        assertEquals("The number of append entries collected should be 1", 1, allMessages.size());
+    }
+
+    @Test
+    public void testMultipleReplicateWithReplyShouldResultInAppendEntries() throws Exception {
+        logStart("testMultipleReplicateWithReplyShouldResultInAppendEntries");
+
+        MockRaftActorContext actorContext = createActorContextWithFollower();
+        actorContext.setConfigParams(new DefaultConfigParamsImpl() {
+            @Override
+            public FiniteDuration getHeartBeatInterval() {
+                return FiniteDuration.apply(5, TimeUnit.SECONDS);
+            }
+        });
+
+        long term = 1;
+        actorContext.getTermInformation().update(term, "");
+
+        leader = new Leader(actorContext);
+
+        // Leader will send an immediate heartbeat - ignore it.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        // The follower would normally reply - simulate that explicitly here.
+        long lastIndex = actorContext.getReplicatedLog().lastIndex();
+        leader.handleMessage(followerActor, new AppendEntriesReply(
+                FOLLOWER_ID, term, true, lastIndex, term, (short)0));
+        assertEquals("isFollowerActive", true, leader.getFollower(FOLLOWER_ID).isFollowerActive());
+
+        followerActor.underlyingActor().clear();
+
+        for(int i=0;i<3;i++) {
+            sendReplicate(actorContext, lastIndex+i+1);
+            leader.handleMessage(followerActor, new AppendEntriesReply(
+                    FOLLOWER_ID, term, true, lastIndex + i + 1, term, (short)0));
+
+        }
+
+        for(int i=3;i<5;i++) {
+            sendReplicate(actorContext, lastIndex + i + 1);
+        }
+
+        List<AppendEntries> allMessages = MessageCollectorActor.getAllMatching(followerActor, AppendEntries.class);
+        // We expect 4 here because the first 3 replicate got a reply and so the 4th entry would
+        // get sent to the follower - but not the 5th
+        assertEquals("The number of append entries collected should be 4", 4, allMessages.size());
+
+        for(int i=0;i<4;i++) {
+            long expected = allMessages.get(i).getEntries().get(0).getIndex();
+            assertEquals(expected, i+2);
+        }
     }
 
+    @Test
+    public void testDuplicateAppendEntriesWillBeSentOnHeartBeat() throws Exception {
+        logStart("testDuplicateAppendEntriesWillBeSentOnHeartBeat");
+
+        MockRaftActorContext actorContext = createActorContextWithFollower();
+        actorContext.setConfigParams(new DefaultConfigParamsImpl() {
+            @Override
+            public FiniteDuration getHeartBeatInterval() {
+                return FiniteDuration.apply(500, TimeUnit.MILLISECONDS);
+            }
+        });
+
+        long term = 1;
+        actorContext.getTermInformation().update(term, "");
+
+        leader = new Leader(actorContext);
+
+        // Leader will send an immediate heartbeat - ignore it.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        // The follower would normally reply - simulate that explicitly here.
+        long lastIndex = actorContext.getReplicatedLog().lastIndex();
+        leader.handleMessage(followerActor, new AppendEntriesReply(
+                FOLLOWER_ID, term, true, lastIndex, term, (short)0));
+        assertEquals("isFollowerActive", true, leader.getFollower(FOLLOWER_ID).isFollowerActive());
+
+        followerActor.underlyingActor().clear();
+
+        sendReplicate(actorContext, lastIndex+1);
+
+        // Wait slightly longer than heartbeat duration
+        Uninterruptibles.sleepUninterruptibly(750, TimeUnit.MILLISECONDS);
+
+        leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
+
+        List<AppendEntries> allMessages = MessageCollectorActor.getAllMatching(followerActor, AppendEntries.class);
+        assertEquals("The number of append entries collected should be 2", 2, allMessages.size());
+
+        assertEquals(1, allMessages.get(0).getEntries().size());
+        assertEquals(lastIndex+1, allMessages.get(0).getEntries().get(0).getIndex());
+        assertEquals(1, allMessages.get(1).getEntries().size());
+        assertEquals(lastIndex+1, allMessages.get(0).getEntries().get(0).getIndex());
+
+    }
+
+    @Test
+    public void testHeartbeatsAreAlwaysSentIfTheHeartbeatIntervalHasElapsed() throws Exception {
+        logStart("testHeartbeatsAreAlwaysSentIfTheHeartbeatIntervalHasElapsed");
+
+        MockRaftActorContext actorContext = createActorContextWithFollower();
+        actorContext.setConfigParams(new DefaultConfigParamsImpl() {
+            @Override
+            public FiniteDuration getHeartBeatInterval() {
+                return FiniteDuration.apply(100, TimeUnit.MILLISECONDS);
+            }
+        });
+
+        long term = 1;
+        actorContext.getTermInformation().update(term, "");
+
+        leader = new Leader(actorContext);
+
+        // Leader will send an immediate heartbeat - ignore it.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        // The follower would normally reply - simulate that explicitly here.
+        long lastIndex = actorContext.getReplicatedLog().lastIndex();
+        leader.handleMessage(followerActor, new AppendEntriesReply(
+                FOLLOWER_ID, term, true, lastIndex, term, (short)0));
+        assertEquals("isFollowerActive", true, leader.getFollower(FOLLOWER_ID).isFollowerActive());
+
+        followerActor.underlyingActor().clear();
+
+        for(int i=0;i<3;i++) {
+            Uninterruptibles.sleepUninterruptibly(150, TimeUnit.MILLISECONDS);
+            leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
+        }
+
+        List<AppendEntries> allMessages = MessageCollectorActor.getAllMatching(followerActor, AppendEntries.class);
+        assertEquals("The number of append entries collected should be 3", 3, allMessages.size());
+    }
+
+    @Test
+    public void testSendingReplicateImmediatelyAfterHeartbeatDoesReplicate() throws Exception {
+        logStart("testSendingReplicateImmediatelyAfterHeartbeatDoesReplicate");
+
+        MockRaftActorContext actorContext = createActorContextWithFollower();
+        actorContext.setConfigParams(new DefaultConfigParamsImpl() {
+            @Override
+            public FiniteDuration getHeartBeatInterval() {
+                return FiniteDuration.apply(100, TimeUnit.MILLISECONDS);
+            }
+        });
+
+        long term = 1;
+        actorContext.getTermInformation().update(term, "");
+
+        leader = new Leader(actorContext);
+
+        // Leader will send an immediate heartbeat - ignore it.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        // The follower would normally reply - simulate that explicitly here.
+        long lastIndex = actorContext.getReplicatedLog().lastIndex();
+        leader.handleMessage(followerActor, new AppendEntriesReply(
+                FOLLOWER_ID, term, true, lastIndex, term, (short)0));
+        assertEquals("isFollowerActive", true, leader.getFollower(FOLLOWER_ID).isFollowerActive());
+
+        followerActor.underlyingActor().clear();
+
+        Uninterruptibles.sleepUninterruptibly(150, TimeUnit.MILLISECONDS);
+        leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
+        sendReplicate(actorContext, lastIndex+1);
+
+        List<AppendEntries> allMessages = MessageCollectorActor.getAllMatching(followerActor, AppendEntries.class);
+        assertEquals("The number of append entries collected should be 2", 2, allMessages.size());
+
+        assertEquals(0, allMessages.get(0).getEntries().size());
+        assertEquals(1, allMessages.get(1).getEntries().size());
+    }
+
+
     @Test
     public void testHandleReplicateMessageWhenThereAreNoFollowers() throws Exception {
         logStart("testHandleReplicateMessageWhenThereAreNoFollowers");
@@ -178,8 +515,8 @@ public class LeaderTest extends AbstractLeaderTest {
 
         actorContext.getReplicatedLog().append(newEntry);
 
-        RaftActorBehavior raftBehavior = leader.handleMessage(leaderActor,
-                new Replicate(leaderActor, "state-id", newEntry));
+        final Identifier id = new MockIdentifier("state-id");
+        RaftActorBehavior raftBehavior = leader.handleMessage(leaderActor, new Replicate(leaderActor, id, newEntry));
 
         // State should not change
         assertTrue(raftBehavior instanceof Leader);
@@ -200,7 +537,7 @@ public class LeaderTest extends AbstractLeaderTest {
 
         ApplyState last = applyStateList.get((int) newLogIndex - 1);
         assertEquals("getData", newEntry.getData(), last.getReplicatedLogEntry().getData());
-        assertEquals("getIdentifier", "state-id", last.getIdentifier());
+        assertEquals("getIdentifier", id, last.getIdentifier());
     }
 
     @Test
@@ -217,8 +554,8 @@ public class LeaderTest extends AbstractLeaderTest {
         //clears leaders log
         actorContext.getReplicatedLog().removeFrom(0);
 
-        final int followersLastIndex = 2;
-        final int snapshotIndex = 3;
+        final int commitIndex = 3;
+        final int snapshotIndex = 2;
         final int newEntryIndex = 4;
         final int snapshotTerm = 1;
         final int currentTerm = 2;
@@ -226,12 +563,15 @@ public class LeaderTest extends AbstractLeaderTest {
         // set the snapshot variables in replicatedlog
         actorContext.getReplicatedLog().setSnapshotIndex(snapshotIndex);
         actorContext.getReplicatedLog().setSnapshotTerm(snapshotTerm);
-        actorContext.setCommitIndex(followersLastIndex);
+        actorContext.setCommitIndex(commitIndex);
         //set follower timeout to 2 mins, helps during debugging
         actorContext.setConfigParams(new MockConfigParamsImpl(120000L, 10));
 
         leader = new Leader(actorContext);
 
+        leader.getFollower(FOLLOWER_ID).setMatchIndex(-1);
+        leader.getFollower(FOLLOWER_ID).setNextIndex(0);
+
         // new entry
         ReplicatedLogImplEntry entry =
                 new ReplicatedLogImplEntry(newEntryIndex, currentTerm,
@@ -241,7 +581,8 @@ public class LeaderTest extends AbstractLeaderTest {
         leader.markFollowerActive(FOLLOWER_ID);
 
         ByteString bs = toByteString(leadersSnapshot);
-        leader.setSnapshot(Optional.of(bs));
+        leader.setSnapshot(Snapshot.create(bs.toByteArray(), Collections.<ReplicatedLogEntry>emptyList(),
+                commitIndex, snapshotTerm, commitIndex, snapshotTerm));
         FollowerToSnapshot fts = leader.new FollowerToSnapshot(bs);
         leader.setFollowerSnapshot(FOLLOWER_ID, fts);
 
@@ -252,7 +593,7 @@ public class LeaderTest extends AbstractLeaderTest {
         Uninterruptibles.sleepUninterruptibly(actorContext.getConfigParams().getHeartBeatInterval().toMillis(),
                 TimeUnit.MILLISECONDS);
 
-        leader.handleMessage(leaderActor, new SendHeartBeat());
+        leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
 
         AppendEntries aeproto = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
 
@@ -263,14 +604,11 @@ public class LeaderTest extends AbstractLeaderTest {
         //InstallSnapshotReply received
         fts.markSendStatus(true);
 
-        leader.handleMessage(leaderActor, new SendHeartBeat());
-
-        InstallSnapshotMessages.InstallSnapshot isproto = MessageCollectorActor.expectFirstMatching(followerActor,
-                InstallSnapshot.SERIALIZABLE_CLASS);
+        leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
 
-        InstallSnapshot is = (InstallSnapshot) SerializationUtils.fromSerializable(isproto);
+        InstallSnapshot is = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
 
-        assertEquals(snapshotIndex, is.getLastIncludedIndex());
+        assertEquals(commitIndex, is.getLastIncludedIndex());
     }
 
     @Test
@@ -308,16 +646,18 @@ public class LeaderTest extends AbstractLeaderTest {
                 new ReplicatedLogImplEntry(newEntryIndex, currentTerm,
                         new MockRaftActorContext.MockPayload("D"));
 
+        actorContext.getReplicatedLog().append(entry);
+
         //update follower timestamp
         leader.markFollowerActive(FOLLOWER_ID);
 
         // this should invoke a sendinstallsnapshot as followersLastIndex < snapshotIndex
         RaftActorBehavior raftBehavior = leader.handleMessage(
-                leaderActor, new Replicate(null, "state-id", entry));
+                leaderActor, new Replicate(null, new MockIdentifier("state-id"), entry));
 
         assertTrue(raftBehavior instanceof Leader);
 
-        MessageCollectorActor.expectFirstMatching(leaderActor, CaptureSnapshot.class);
+        assertEquals("isCapturing", true, actorContext.getSnapshotManager().isCapturing());
     }
 
     @Test
@@ -326,11 +666,6 @@ public class LeaderTest extends AbstractLeaderTest {
 
         MockRaftActorContext actorContext = createActorContextWithFollower();
 
-        Map<String, String> leadersSnapshot = new HashMap<>();
-        leadersSnapshot.put("1", "A");
-        leadersSnapshot.put("2", "B");
-        leadersSnapshot.put("3", "C");
-
         //clears leaders log
         actorContext.getReplicatedLog().removeFrom(0);
 
@@ -352,7 +687,7 @@ public class LeaderTest extends AbstractLeaderTest {
         MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
 
         // set the snapshot as absent and check if capture-snapshot is invoked.
-        leader.setSnapshot(Optional.<ByteString>absent());
+        leader.setSnapshot(null);
 
         // new entry
         ReplicatedLogImplEntry entry = new ReplicatedLogImplEntry(newEntryIndex, currentTerm,
@@ -363,9 +698,11 @@ public class LeaderTest extends AbstractLeaderTest {
         //update follower timestamp
         leader.markFollowerActive(FOLLOWER_ID);
 
-        leader.handleMessage(leaderActor, new Replicate(null, "state-id", entry));
+        leader.handleMessage(leaderActor, new Replicate(null, new MockIdentifier("state-id"), entry));
+
+        assertEquals("isCapturing", true, actorContext.getSnapshotManager().isCapturing());
 
-        CaptureSnapshot cs = MessageCollectorActor.expectFirstMatching(leaderActor, CaptureSnapshot.class);
+        CaptureSnapshot cs = actorContext.getSnapshotManager().getCaptureSnapshot();
 
         assertTrue(cs.isInstallSnapshotInitiated());
         assertEquals(3, cs.getLastAppliedIndex());
@@ -374,55 +711,173 @@ public class LeaderTest extends AbstractLeaderTest {
         assertEquals(2, cs.getLastTerm());
 
         // if an initiate is started again when first is in progress, it shouldnt initiate Capture
-        leader.handleMessage(leaderActor, new Replicate(null, "state-id", entry));
+        leader.handleMessage(leaderActor, new Replicate(null, new MockIdentifier("state-id"), entry));
 
-        List<CaptureSnapshot> captureSnapshots = MessageCollectorActor.getAllMatching(leaderActor, CaptureSnapshot.class);
-        assertEquals("CaptureSnapshot should not get invoked when  initiate is in progress", 1, captureSnapshots.size());
+        assertSame("CaptureSnapshot instance", cs, actorContext.getSnapshotManager().getCaptureSnapshot());
     }
 
     @Test
-    public void testInstallSnapshot() throws Exception {
-        logStart("testInstallSnapshot");
+    public void testInitiateForceInstallSnapshot() throws Exception {
+        logStart("testInitiateForceInstallSnapshot");
 
         MockRaftActorContext actorContext = createActorContextWithFollower();
 
-        Map<String, String> leadersSnapshot = new HashMap<>();
-        leadersSnapshot.put("1", "A");
-        leadersSnapshot.put("2", "B");
-        leadersSnapshot.put("3", "C");
-
-        //clears leaders log
-        actorContext.getReplicatedLog().removeFrom(0);
-
         final int followersLastIndex = 2;
-        final int snapshotIndex = 3;
-        final int snapshotTerm = 1;
+        final int snapshotIndex = -1;
+        final int newEntryIndex = 4;
+        final int snapshotTerm = -1;
         final int currentTerm = 2;
 
         // set the snapshot variables in replicatedlog
         actorContext.getReplicatedLog().setSnapshotIndex(snapshotIndex);
         actorContext.getReplicatedLog().setSnapshotTerm(snapshotTerm);
-        actorContext.getTermInformation().update(currentTerm, leaderActor.path().toString());
+        actorContext.setLastApplied(3);
         actorContext.setCommitIndex(followersLastIndex);
 
+        actorContext.getReplicatedLog().removeFrom(0);
+
         leader = new Leader(actorContext);
 
-        // Ignore initial heartbeat.
+        // Leader will send an immediate heartbeat - ignore it.
         MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
 
-        RaftActorBehavior raftBehavior = leader.handleMessage(leaderActor,
-                new SendInstallSnapshot(toByteString(leadersSnapshot)));
-
-        assertTrue(raftBehavior instanceof Leader);
+        // set the snapshot as absent and check if capture-snapshot is invoked.
+        leader.setSnapshot(null);
 
-        // check if installsnapshot gets called with the correct values.
+        for(int i=0;i<4;i++) {
+            actorContext.getReplicatedLog().append(new ReplicatedLogImplEntry(i, 1,
+                    new MockRaftActorContext.MockPayload("X" + i)));
+        }
 
-        InstallSnapshot installSnapshot = (InstallSnapshot) SerializationUtils.fromSerializable(
-                MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshotMessages.InstallSnapshot.class));
+        // new entry
+        ReplicatedLogImplEntry entry = new ReplicatedLogImplEntry(newEntryIndex, currentTerm,
+                new MockRaftActorContext.MockPayload("D"));
 
-        assertNotNull(installSnapshot.getData());
-        assertEquals(snapshotIndex, installSnapshot.getLastIncludedIndex());
-        assertEquals(snapshotTerm, installSnapshot.getLastIncludedTerm());
+        actorContext.getReplicatedLog().append(entry);
+
+        //update follower timestamp
+        leader.markFollowerActive(FOLLOWER_ID);
+
+        // Sending this AppendEntriesReply forces the Leader to capture a snapshot, which subsequently gets
+        // installed with a SendInstallSnapshot
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, false, 100, 1, (short) 1, true));
+
+        assertEquals("isCapturing", true, actorContext.getSnapshotManager().isCapturing());
+
+        CaptureSnapshot cs = actorContext.getSnapshotManager().getCaptureSnapshot();
+
+        assertTrue(cs.isInstallSnapshotInitiated());
+        assertEquals(3, cs.getLastAppliedIndex());
+        assertEquals(1, cs.getLastAppliedTerm());
+        assertEquals(4, cs.getLastIndex());
+        assertEquals(2, cs.getLastTerm());
+
+        // if an initiate is started again when first is in progress, it should not initiate Capture
+        leader.handleMessage(leaderActor, new Replicate(null, new MockIdentifier("state-id"), entry));
+
+        assertSame("CaptureSnapshot instance", cs, actorContext.getSnapshotManager().getCaptureSnapshot());
+    }
+
+
+    @Test
+    public void testInstallSnapshot() throws Exception {
+        logStart("testInstallSnapshot");
+
+        MockRaftActorContext actorContext = createActorContextWithFollower();
+
+        Map<String, String> leadersSnapshot = new HashMap<>();
+        leadersSnapshot.put("1", "A");
+        leadersSnapshot.put("2", "B");
+        leadersSnapshot.put("3", "C");
+
+        //clears leaders log
+        actorContext.getReplicatedLog().removeFrom(0);
+
+        final int lastAppliedIndex = 3;
+        final int snapshotIndex = 2;
+        final int snapshotTerm = 1;
+        final int currentTerm = 2;
+
+        // set the snapshot variables in replicatedlog
+        actorContext.getReplicatedLog().setSnapshotIndex(snapshotIndex);
+        actorContext.getReplicatedLog().setSnapshotTerm(snapshotTerm);
+        actorContext.getTermInformation().update(currentTerm, leaderActor.path().toString());
+        actorContext.setCommitIndex(lastAppliedIndex);
+        actorContext.setLastApplied(lastAppliedIndex);
+
+        leader = new Leader(actorContext);
+
+        // Initial heartbeat.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        leader.getFollower(FOLLOWER_ID).setMatchIndex(-1);
+        leader.getFollower(FOLLOWER_ID).setNextIndex(0);
+
+        Snapshot snapshot = Snapshot.create(toByteString(leadersSnapshot).toByteArray(),
+                Collections.<ReplicatedLogEntry>emptyList(),
+                lastAppliedIndex, snapshotTerm, lastAppliedIndex, snapshotTerm);
+
+        RaftActorBehavior raftBehavior = leader.handleMessage(leaderActor, new SendInstallSnapshot(snapshot));
+
+        assertTrue(raftBehavior instanceof Leader);
+
+        // check if installsnapshot gets called with the correct values.
+
+        InstallSnapshot installSnapshot = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
+
+        assertNotNull(installSnapshot.getData());
+        assertEquals(lastAppliedIndex, installSnapshot.getLastIncludedIndex());
+        assertEquals(snapshotTerm, installSnapshot.getLastIncludedTerm());
+
+        assertEquals(currentTerm, installSnapshot.getTerm());
+    }
+
+    @Test
+    public void testForceInstallSnapshot() throws Exception {
+        logStart("testForceInstallSnapshot");
+
+        MockRaftActorContext actorContext = createActorContextWithFollower();
+
+        Map<String, String> leadersSnapshot = new HashMap<>();
+        leadersSnapshot.put("1", "A");
+        leadersSnapshot.put("2", "B");
+        leadersSnapshot.put("3", "C");
+
+        final int lastAppliedIndex = 3;
+        final int snapshotIndex = -1;
+        final int snapshotTerm = -1;
+        final int currentTerm = 2;
+
+        // set the snapshot variables in replicatedlog
+        actorContext.getReplicatedLog().setSnapshotIndex(snapshotIndex);
+        actorContext.getReplicatedLog().setSnapshotTerm(snapshotTerm);
+        actorContext.getTermInformation().update(currentTerm, leaderActor.path().toString());
+        actorContext.setCommitIndex(lastAppliedIndex);
+        actorContext.setLastApplied(lastAppliedIndex);
+
+        leader = new Leader(actorContext);
+
+        // Initial heartbeat.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        leader.getFollower(FOLLOWER_ID).setMatchIndex(-1);
+        leader.getFollower(FOLLOWER_ID).setNextIndex(-1);
+
+        Snapshot snapshot = Snapshot.create(toByteString(leadersSnapshot).toByteArray(),
+                Collections.<ReplicatedLogEntry>emptyList(),
+                lastAppliedIndex, snapshotTerm, lastAppliedIndex, snapshotTerm);
+
+        RaftActorBehavior raftBehavior = leader.handleMessage(leaderActor, new SendInstallSnapshot(snapshot));
+
+        assertTrue(raftBehavior instanceof Leader);
+
+        // check if installsnapshot gets called with the correct values.
+
+        InstallSnapshot installSnapshot = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
+
+        assertNotNull(installSnapshot.getData());
+        assertEquals(lastAppliedIndex, installSnapshot.getLastIncludedIndex());
+        assertEquals(snapshotTerm, installSnapshot.getLastIncludedTerm());
 
         assertEquals(currentTerm, installSnapshot.getTerm());
     }
@@ -433,14 +888,18 @@ public class LeaderTest extends AbstractLeaderTest {
 
         MockRaftActorContext actorContext = createActorContextWithFollower();
 
-        final int followersLastIndex = 2;
-        final int snapshotIndex = 3;
+        final int commitIndex = 3;
+        final int snapshotIndex = 2;
         final int snapshotTerm = 1;
         final int currentTerm = 2;
 
-        actorContext.setCommitIndex(followersLastIndex);
+        actorContext.setCommitIndex(commitIndex);
 
         leader = new Leader(actorContext);
+        actorContext.setCurrentBehavior(leader);
+
+        leader.getFollower(FOLLOWER_ID).setMatchIndex(-1);
+        leader.getFollower(FOLLOWER_ID).setNextIndex(0);
 
         // Ignore initial heartbeat.
         MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
@@ -457,7 +916,8 @@ public class LeaderTest extends AbstractLeaderTest {
         actorContext.getTermInformation().update(currentTerm, leaderActor.path().toString());
 
         ByteString bs = toByteString(leadersSnapshot);
-        leader.setSnapshot(Optional.of(bs));
+        leader.setSnapshot(Snapshot.create(bs.toByteArray(), Collections.<ReplicatedLogEntry>emptyList(),
+                commitIndex, snapshotTerm, commitIndex, snapshotTerm));
         FollowerToSnapshot fts = leader.new FollowerToSnapshot(bs);
         leader.setFollowerSnapshot(FOLLOWER_ID, fts);
         while(!fts.isLastChunk(fts.getChunkIndex())) {
@@ -477,9 +937,8 @@ public class LeaderTest extends AbstractLeaderTest {
         assertEquals(1, leader.followerLogSize());
         FollowerLogInformation fli = leader.getFollower(FOLLOWER_ID);
         assertNotNull(fli);
-        assertEquals(snapshotIndex, fli.getMatchIndex());
-        assertEquals(snapshotIndex, fli.getMatchIndex());
-        assertEquals(snapshotIndex + 1, fli.getNextIndex());
+        assertEquals(commitIndex, fli.getMatchIndex());
+        assertEquals(commitIndex + 1, fli.getNextIndex());
     }
 
     @Test
@@ -488,8 +947,8 @@ public class LeaderTest extends AbstractLeaderTest {
 
         MockRaftActorContext actorContext = createActorContextWithFollower();
 
-        final int followersLastIndex = 2;
-        final int snapshotIndex = 3;
+        final int commitIndex = 3;
+        final int snapshotIndex = 2;
         final int snapshotTerm = 1;
         final int currentTerm = 2;
 
@@ -503,9 +962,13 @@ public class LeaderTest extends AbstractLeaderTest {
         configParams.setIsolatedLeaderCheckInterval(new FiniteDuration(10, TimeUnit.SECONDS));
 
         actorContext.setConfigParams(configParams);
-        actorContext.setCommitIndex(followersLastIndex);
+        actorContext.setCommitIndex(commitIndex);
 
         leader = new Leader(actorContext);
+        actorContext.setCurrentBehavior(leader);
+
+        leader.getFollower(FOLLOWER_ID).setMatchIndex(-1);
+        leader.getFollower(FOLLOWER_ID).setNextIndex(0);
 
         Map<String, String> leadersSnapshot = new HashMap<>();
         leadersSnapshot.put("1", "A");
@@ -518,12 +981,13 @@ public class LeaderTest extends AbstractLeaderTest {
         actorContext.getTermInformation().update(currentTerm, leaderActor.path().toString());
 
         ByteString bs = toByteString(leadersSnapshot);
-        leader.setSnapshot(Optional.of(bs));
+        Snapshot snapshot = Snapshot.create(bs.toByteArray(), Collections.<ReplicatedLogEntry>emptyList(),
+                commitIndex, snapshotTerm, commitIndex, snapshotTerm);
+        leader.setSnapshot(snapshot);
 
-        leader.handleMessage(leaderActor, new SendInstallSnapshot(bs));
+        leader.handleMessage(leaderActor, new SendInstallSnapshot(snapshot));
 
-        InstallSnapshotMessages.InstallSnapshot installSnapshot = MessageCollectorActor.expectFirstMatching(
-                followerActor, InstallSnapshotMessages.InstallSnapshot.class);
+        InstallSnapshot installSnapshot = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
 
         assertEquals(1, installSnapshot.getChunkIndex());
         assertEquals(3, installSnapshot.getTotalChunks());
@@ -532,8 +996,7 @@ public class LeaderTest extends AbstractLeaderTest {
         leader.handleMessage(followerActor, new InstallSnapshotReply(actorContext.getTermInformation().getCurrentTerm(),
                 FOLLOWER_ID, installSnapshot.getChunkIndex(), true));
 
-        installSnapshot = MessageCollectorActor.expectFirstMatching(
-                followerActor, InstallSnapshotMessages.InstallSnapshot.class);
+        installSnapshot = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
 
         assertEquals(2, installSnapshot.getChunkIndex());
         assertEquals(3, installSnapshot.getTotalChunks());
@@ -542,18 +1005,16 @@ public class LeaderTest extends AbstractLeaderTest {
         leader.handleMessage(followerActor, new InstallSnapshotReply(actorContext.getTermInformation().getCurrentTerm(),
                 FOLLOWER_ID, installSnapshot.getChunkIndex(), true));
 
-        installSnapshot = MessageCollectorActor.expectFirstMatching(
-                followerActor, InstallSnapshotMessages.InstallSnapshot.class);
+        installSnapshot = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
 
         // Send snapshot reply one more time and make sure that a new snapshot message should not be sent to follower
         followerActor.underlyingActor().clear();
         leader.handleMessage(followerActor, new InstallSnapshotReply(actorContext.getTermInformation().getCurrentTerm(),
                 FOLLOWER_ID, installSnapshot.getChunkIndex(), true));
 
-        installSnapshot = MessageCollectorActor.getFirstMatching(
-                followerActor, InstallSnapshotMessages.InstallSnapshot.class);
+        installSnapshot = MessageCollectorActor.getFirstMatching(followerActor, InstallSnapshot.class);
 
-        Assert.assertNull(installSnapshot);
+        assertNull(installSnapshot);
     }
 
 
@@ -563,8 +1024,8 @@ public class LeaderTest extends AbstractLeaderTest {
 
         MockRaftActorContext actorContext = createActorContextWithFollower();
 
-        final int followersLastIndex = 2;
-        final int snapshotIndex = 3;
+        final int commitIndex = 3;
+        final int snapshotIndex = 2;
         final int snapshotTerm = 1;
         final int currentTerm = 2;
 
@@ -575,10 +1036,13 @@ public class LeaderTest extends AbstractLeaderTest {
             }
         });
 
-        actorContext.setCommitIndex(followersLastIndex);
+        actorContext.setCommitIndex(commitIndex);
 
         leader = new Leader(actorContext);
 
+        leader.getFollower(FOLLOWER_ID).setMatchIndex(-1);
+        leader.getFollower(FOLLOWER_ID).setNextIndex(0);
+
         Map<String, String> leadersSnapshot = new HashMap<>();
         leadersSnapshot.put("1", "A");
         leadersSnapshot.put("2", "B");
@@ -590,12 +1054,14 @@ public class LeaderTest extends AbstractLeaderTest {
         actorContext.getTermInformation().update(currentTerm, leaderActor.path().toString());
 
         ByteString bs = toByteString(leadersSnapshot);
-        leader.setSnapshot(Optional.of(bs));
+        Snapshot snapshot = Snapshot.create(bs.toByteArray(), Collections.<ReplicatedLogEntry>emptyList(),
+                commitIndex, snapshotTerm, commitIndex, snapshotTerm);
+        leader.setSnapshot(snapshot);
 
-        leader.handleMessage(leaderActor, new SendInstallSnapshot(bs));
+        Uninterruptibles.sleepUninterruptibly(1, TimeUnit.SECONDS);
+        leader.handleMessage(leaderActor, new SendInstallSnapshot(snapshot));
 
-        InstallSnapshotMessages.InstallSnapshot installSnapshot = MessageCollectorActor.expectFirstMatching(
-                followerActor, InstallSnapshotMessages.InstallSnapshot.class);
+        InstallSnapshot installSnapshot = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
 
         assertEquals(1, installSnapshot.getChunkIndex());
         assertEquals(3, installSnapshot.getTotalChunks());
@@ -608,10 +1074,9 @@ public class LeaderTest extends AbstractLeaderTest {
         Uninterruptibles.sleepUninterruptibly(actorContext.getConfigParams().getHeartBeatInterval().toMillis(),
                 TimeUnit.MILLISECONDS);
 
-        leader.handleMessage(leaderActor, new SendHeartBeat());
+        leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
 
-        installSnapshot = MessageCollectorActor.expectFirstMatching(
-                followerActor, InstallSnapshotMessages.InstallSnapshot.class);
+        installSnapshot = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
 
         assertEquals(1, installSnapshot.getChunkIndex());
         assertEquals(3, installSnapshot.getTotalChunks());
@@ -623,8 +1088,8 @@ public class LeaderTest extends AbstractLeaderTest {
 
         MockRaftActorContext actorContext = createActorContextWithFollower();
 
-        final int followersLastIndex = 2;
-        final int snapshotIndex = 3;
+        final int commitIndex = 3;
+        final int snapshotIndex = 2;
         final int snapshotTerm = 1;
         final int currentTerm = 2;
 
@@ -635,10 +1100,13 @@ public class LeaderTest extends AbstractLeaderTest {
             }
         });
 
-        actorContext.setCommitIndex(followersLastIndex);
+        actorContext.setCommitIndex(commitIndex);
 
         leader = new Leader(actorContext);
 
+        leader.getFollower(FOLLOWER_ID).setMatchIndex(-1);
+        leader.getFollower(FOLLOWER_ID).setNextIndex(0);
+
         Map<String, String> leadersSnapshot = new HashMap<>();
         leadersSnapshot.put("1", "A");
         leadersSnapshot.put("2", "B");
@@ -650,30 +1118,30 @@ public class LeaderTest extends AbstractLeaderTest {
         actorContext.getTermInformation().update(currentTerm, leaderActor.path().toString());
 
         ByteString bs = toByteString(leadersSnapshot);
-        leader.setSnapshot(Optional.of(bs));
+        Snapshot snapshot = Snapshot.create(bs.toByteArray(), Collections.<ReplicatedLogEntry>emptyList(),
+                commitIndex, snapshotTerm, commitIndex, snapshotTerm);
+        leader.setSnapshot(snapshot);
 
-        leader.handleMessage(leaderActor, new SendInstallSnapshot(bs));
+        leader.handleMessage(leaderActor, new SendInstallSnapshot(snapshot));
 
-        InstallSnapshotMessages.InstallSnapshot installSnapshot = MessageCollectorActor.expectFirstMatching(
-                followerActor, InstallSnapshotMessages.InstallSnapshot.class);
+        InstallSnapshot installSnapshot = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
 
         assertEquals(1, installSnapshot.getChunkIndex());
         assertEquals(3, installSnapshot.getTotalChunks());
-        assertEquals(AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE, installSnapshot.getLastChunkHashCode());
+        assertEquals(AbstractLeader.INITIAL_LAST_CHUNK_HASH_CODE, installSnapshot.getLastChunkHashCode().get().intValue());
 
-        int hashCode = installSnapshot.getData().hashCode();
+        int hashCode = Arrays.hashCode(installSnapshot.getData());
 
         followerActor.underlyingActor().clear();
 
         leader.handleMessage(followerActor, new InstallSnapshotReply(installSnapshot.getTerm(),
                 FOLLOWER_ID, 1, true));
 
-        installSnapshot = MessageCollectorActor.expectFirstMatching(
-                followerActor, InstallSnapshotMessages.InstallSnapshot.class);
+        installSnapshot = MessageCollectorActor.expectFirstMatching(followerActor, InstallSnapshot.class);
 
         assertEquals(2, installSnapshot.getChunkIndex());
         assertEquals(3, installSnapshot.getTotalChunks());
-        assertEquals(hashCode, installSnapshot.getLastChunkHashCode());
+        assertEquals(hashCode, installSnapshot.getLastChunkHashCode().get().intValue());
     }
 
     @Test
@@ -713,8 +1181,8 @@ public class LeaderTest extends AbstractLeaderTest {
                 j = barray.length;
             }
 
-            ByteString chunk = fts.getNextChunk();
-            assertEquals("bytestring size not matching for chunk:"+ chunkIndex, j-i, chunk.size());
+            byte[] chunk = fts.getNextChunk();
+            assertEquals("bytestring size not matching for chunk:"+ chunkIndex, j-i, chunk.length);
             assertEquals("chunkindex not matching", chunkIndex, fts.getChunkIndex());
 
             fts.markSendStatus(true);
@@ -726,8 +1194,8 @@ public class LeaderTest extends AbstractLeaderTest {
         assertEquals("totalChunks not matching", chunkIndex, fts.getTotalChunks());
     }
 
-    @Override protected RaftActorBehavior createBehavior(
-        RaftActorContext actorContext) {
+    @Override
+    protected Leader createBehavior(final RaftActorContext actorContext) {
         return new Leader(actorContext);
     }
 
@@ -738,7 +1206,7 @@ public class LeaderTest extends AbstractLeaderTest {
 
     @Override
     protected MockRaftActorContext createActorContext(ActorRef actorRef) {
-        return createActorContext("leader", actorRef);
+        return createActorContext(LEADER_ID, actorRef);
     }
 
     private MockRaftActorContext createActorContextWithFollower() {
@@ -754,9 +1222,19 @@ public class LeaderTest extends AbstractLeaderTest {
         configParams.setElectionTimeoutFactor(100000);
         MockRaftActorContext context = new MockRaftActorContext(id, getSystem(), actorRef);
         context.setConfigParams(configParams);
+        context.setPayloadVersion(payloadVersion);
         return context;
     }
 
+    private MockRaftActorContext createFollowerActorContextWithLeader() {
+        MockRaftActorContext followerActorContext = createActorContext(FOLLOWER_ID, followerActor);
+        DefaultConfigParamsImpl followerConfig = new DefaultConfigParamsImpl();
+        followerConfig.setElectionTimeoutFactor(10000);
+        followerActorContext.setConfigParams(followerConfig);
+        followerActorContext.setPeerAddresses(ImmutableMap.of(LEADER_ID, leaderActor.path().toString()));
+        return followerActorContext;
+    }
+
     @Test
     public void testLeaderCreatedWithCommitIndexLessThanLastIndex() throws Exception {
         logStart("testLeaderCreatedWithCommitIndexLessThanLastIndex");
@@ -767,6 +1245,7 @@ public class LeaderTest extends AbstractLeaderTest {
 
         Follower follower = new Follower(followerActorContext);
         followerActor.underlyingActor().setBehavior(follower);
+        followerActorContext.setCurrentBehavior(follower);
 
         Map<String, String> peerAddresses = new HashMap<>();
         peerAddresses.put(FOLLOWER_ID, followerActor.path().toString());
@@ -790,6 +1269,7 @@ public class LeaderTest extends AbstractLeaderTest {
         followerActorContext.setCommitIndex(1);
 
         leader = new Leader(leaderActorContext);
+        leaderActorContext.setCurrentBehavior(leader);
 
         AppendEntries appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
 
@@ -817,14 +1297,16 @@ public class LeaderTest extends AbstractLeaderTest {
         MockRaftActorContext leaderActorContext = createActorContext();
 
         MockRaftActorContext followerActorContext = createActorContext(FOLLOWER_ID, followerActor);
+        followerActorContext.setPeerAddresses(ImmutableMap.of(LEADER_ID, leaderActor.path().toString()));
 
         Follower follower = new Follower(followerActorContext);
         followerActor.underlyingActor().setBehavior(follower);
+        followerActorContext.setCurrentBehavior(follower);
 
-        Map<String, String> peerAddresses = new HashMap<>();
-        peerAddresses.put(FOLLOWER_ID, followerActor.path().toString());
+        Map<String, String> leaderPeerAddresses = new HashMap<>();
+        leaderPeerAddresses.put(FOLLOWER_ID, followerActor.path().toString());
 
-        leaderActorContext.setPeerAddresses(peerAddresses);
+        leaderActorContext.setPeerAddresses(leaderPeerAddresses);
 
         leaderActorContext.getReplicatedLog().removeFrom(0);
 
@@ -865,7 +1347,7 @@ public class LeaderTest extends AbstractLeaderTest {
         Uninterruptibles.sleepUninterruptibly(leaderActorContext.getConfigParams().getHeartBeatInterval().toMillis(),
                 TimeUnit.MILLISECONDS);
 
-        leader.handleMessage(leaderActor, new SendHeartBeat());
+        leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
 
         appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
 
@@ -884,26 +1366,293 @@ public class LeaderTest extends AbstractLeaderTest {
     }
 
     @Test
-    public void testHandleAppendEntriesReplyFailure(){
-        logStart("testHandleAppendEntriesReplyFailure");
+    public void testHandleAppendEntriesReplyFailureWithFollowersLogBehindTheLeader(){
+        logStart("testHandleAppendEntriesReplyFailureWithFollowersLogBehindTheLeader");
 
         MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(1000, TimeUnit.SECONDS));
+
+        leaderActorContext.setReplicatedLog(
+                new MockRaftActorContext.MockReplicatedLogBuilder().createEntries(0, 3, 1).build());
+        long leaderCommitIndex = 2;
+        leaderActorContext.setCommitIndex(leaderCommitIndex);
+        leaderActorContext.setLastApplied(leaderCommitIndex);
+
+        ReplicatedLogEntry leadersSecondLogEntry = leaderActorContext.getReplicatedLog().get(1);
+        ReplicatedLogEntry leadersThirdLogEntry = leaderActorContext.getReplicatedLog().get(2);
+
+        MockRaftActorContext followerActorContext = createFollowerActorContextWithLeader();
+
+        followerActorContext.setReplicatedLog(
+                new MockRaftActorContext.MockReplicatedLogBuilder().createEntries(0, 1, 1).build());
+        followerActorContext.setCommitIndex(0);
+        followerActorContext.setLastApplied(0);
+
+        Follower follower = new Follower(followerActorContext);
+        followerActor.underlyingActor().setBehavior(follower);
 
         leader = new Leader(leaderActorContext);
 
-        // Send initial heartbeat reply with last index.
-        leader.handleAppendEntriesReply(followerActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, 10, 1));
+        AppendEntries appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        AppendEntriesReply appendEntriesReply = MessageCollectorActor.expectFirstMatching(leaderActor, AppendEntriesReply.class);
+
+        MessageCollectorActor.clearMessages(followerActor);
+        MessageCollectorActor.clearMessages(leaderActor);
+
+        // Verify initial AppendEntries sent with the leader's current commit index.
+        assertEquals("getLeaderCommit", leaderCommitIndex, appendEntries.getLeaderCommit());
+        assertEquals("Log entries size", 0, appendEntries.getEntries().size());
+        assertEquals("getPrevLogIndex", 1, appendEntries.getPrevLogIndex());
+
+        leaderActor.underlyingActor().setBehavior(leader);
+
+        leader.handleMessage(followerActor, appendEntriesReply);
+
+        MessageCollectorActor.expectMatching(leaderActor, AppendEntriesReply.class, 1);
+        appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        assertEquals("getLeaderCommit", leaderCommitIndex, appendEntries.getLeaderCommit());
+        assertEquals("getPrevLogIndex", -1, appendEntries.getPrevLogIndex());
+        assertEquals("Log entries size", 2, appendEntries.getEntries().size());
+
+        assertEquals("First entry index", 1, appendEntries.getEntries().get(0).getIndex());
+        assertEquals("First entry data", leadersSecondLogEntry.getData(),
+                appendEntries.getEntries().get(0).getData());
+        assertEquals("Second entry index", 2, appendEntries.getEntries().get(1).getIndex());
+        assertEquals("Second entry data", leadersThirdLogEntry.getData(),
+                appendEntries.getEntries().get(1).getData());
 
         FollowerLogInformation followerInfo = leader.getFollower(FOLLOWER_ID);
-        assertEquals("getNextIndex", 11, followerInfo.getNextIndex());
+        assertEquals("getNextIndex", 3, followerInfo.getNextIndex());
 
-        AppendEntriesReply reply = new AppendEntriesReply(FOLLOWER_ID, 1, false, 10, 1);
+        List<ApplyState> applyStateList = MessageCollectorActor.expectMatching(followerActor, ApplyState.class, 2);
 
-        RaftActorBehavior raftActorBehavior = leader.handleAppendEntriesReply(followerActor, reply);
+        ApplyState applyState = applyStateList.get(0);
+        assertEquals("Follower's first ApplyState index", 1, applyState.getReplicatedLogEntry().getIndex());
+        assertEquals("Follower's first ApplyState term", 1, applyState.getReplicatedLogEntry().getTerm());
+        assertEquals("Follower's first ApplyState data", leadersSecondLogEntry.getData(),
+                applyState.getReplicatedLogEntry().getData());
+
+        applyState = applyStateList.get(1);
+        assertEquals("Follower's second ApplyState index", 2, applyState.getReplicatedLogEntry().getIndex());
+        assertEquals("Follower's second ApplyState term", 1, applyState.getReplicatedLogEntry().getTerm());
+        assertEquals("Follower's second ApplyState data", leadersThirdLogEntry.getData(),
+                applyState.getReplicatedLogEntry().getData());
+
+        assertEquals("Follower's commit index", 2, followerActorContext.getCommitIndex());
+        assertEquals("Follower's lastIndex", 2, followerActorContext.getReplicatedLog().lastIndex());
+    }
 
-        assertEquals(RaftState.Leader, raftActorBehavior.state());
+    @Test
+    public void testHandleAppendEntriesReplyFailureWithFollowersLogEmpty() {
+        logStart("testHandleAppendEntriesReplyFailureWithFollowersLogEmpty");
+
+        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(1000, TimeUnit.SECONDS));
+
+        leaderActorContext.setReplicatedLog(
+                new MockRaftActorContext.MockReplicatedLogBuilder().createEntries(0, 2, 1).build());
+        long leaderCommitIndex = 1;
+        leaderActorContext.setCommitIndex(leaderCommitIndex);
+        leaderActorContext.setLastApplied(leaderCommitIndex);
+
+        ReplicatedLogEntry leadersFirstLogEntry = leaderActorContext.getReplicatedLog().get(0);
+        ReplicatedLogEntry leadersSecondLogEntry = leaderActorContext.getReplicatedLog().get(1);
+
+        MockRaftActorContext followerActorContext = createFollowerActorContextWithLeader();
+
+        followerActorContext.setReplicatedLog(new MockRaftActorContext.MockReplicatedLogBuilder().build());
+        followerActorContext.setCommitIndex(-1);
+        followerActorContext.setLastApplied(-1);
+
+        Follower follower = new Follower(followerActorContext);
+        followerActor.underlyingActor().setBehavior(follower);
+        followerActorContext.setCurrentBehavior(follower);
+
+        leader = new Leader(leaderActorContext);
+
+        AppendEntries appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        AppendEntriesReply appendEntriesReply = MessageCollectorActor.expectFirstMatching(leaderActor, AppendEntriesReply.class);
+
+        MessageCollectorActor.clearMessages(followerActor);
+        MessageCollectorActor.clearMessages(leaderActor);
+
+        // Verify initial AppendEntries sent with the leader's current commit index.
+        assertEquals("getLeaderCommit", leaderCommitIndex, appendEntries.getLeaderCommit());
+        assertEquals("Log entries size", 0, appendEntries.getEntries().size());
+        assertEquals("getPrevLogIndex", 0, appendEntries.getPrevLogIndex());
+
+        leaderActor.underlyingActor().setBehavior(leader);
+        leaderActorContext.setCurrentBehavior(leader);
+
+        leader.handleMessage(followerActor, appendEntriesReply);
+
+        MessageCollectorActor.expectMatching(leaderActor, AppendEntriesReply.class, 1);
+        appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        assertEquals("getLeaderCommit", leaderCommitIndex, appendEntries.getLeaderCommit());
+        assertEquals("getPrevLogIndex", -1, appendEntries.getPrevLogIndex());
+        assertEquals("Log entries size", 2, appendEntries.getEntries().size());
+
+        assertEquals("First entry index", 0, appendEntries.getEntries().get(0).getIndex());
+        assertEquals("First entry data", leadersFirstLogEntry.getData(),
+                appendEntries.getEntries().get(0).getData());
+        assertEquals("Second entry index", 1, appendEntries.getEntries().get(1).getIndex());
+        assertEquals("Second entry data", leadersSecondLogEntry.getData(),
+                appendEntries.getEntries().get(1).getData());
+
+        FollowerLogInformation followerInfo = leader.getFollower(FOLLOWER_ID);
+        assertEquals("getNextIndex", 2, followerInfo.getNextIndex());
+
+        List<ApplyState> applyStateList = MessageCollectorActor.expectMatching(followerActor, ApplyState.class, 2);
+
+        ApplyState applyState = applyStateList.get(0);
+        assertEquals("Follower's first ApplyState index", 0, applyState.getReplicatedLogEntry().getIndex());
+        assertEquals("Follower's first ApplyState term", 1, applyState.getReplicatedLogEntry().getTerm());
+        assertEquals("Follower's first ApplyState data", leadersFirstLogEntry.getData(),
+                applyState.getReplicatedLogEntry().getData());
+
+        applyState = applyStateList.get(1);
+        assertEquals("Follower's second ApplyState index", 1, applyState.getReplicatedLogEntry().getIndex());
+        assertEquals("Follower's second ApplyState term", 1, applyState.getReplicatedLogEntry().getTerm());
+        assertEquals("Follower's second ApplyState data", leadersSecondLogEntry.getData(),
+                applyState.getReplicatedLogEntry().getData());
+
+        assertEquals("Follower's commit index", 1, followerActorContext.getCommitIndex());
+        assertEquals("Follower's lastIndex", 1, followerActorContext.getReplicatedLog().lastIndex());
+    }
+
+    @Test
+    public void testHandleAppendEntriesReplyFailureWithFollowersLogTermDifferent(){
+        logStart("testHandleAppendEntriesReplyFailureWithFollowersLogTermDifferent");
+
+        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(1000, TimeUnit.SECONDS));
+
+        leaderActorContext.setReplicatedLog(
+                new MockRaftActorContext.MockReplicatedLogBuilder().createEntries(0, 2, 2).build());
+        long leaderCommitIndex = 1;
+        leaderActorContext.setCommitIndex(leaderCommitIndex);
+        leaderActorContext.setLastApplied(leaderCommitIndex);
+
+        ReplicatedLogEntry leadersFirstLogEntry = leaderActorContext.getReplicatedLog().get(0);
+        ReplicatedLogEntry leadersSecondLogEntry = leaderActorContext.getReplicatedLog().get(1);
+
+        MockRaftActorContext followerActorContext = createFollowerActorContextWithLeader();
+
+        followerActorContext.setReplicatedLog(
+                new MockRaftActorContext.MockReplicatedLogBuilder().createEntries(0, 1, 1).build());
+        followerActorContext.setCommitIndex(-1);
+        followerActorContext.setLastApplied(-1);
+
+        Follower follower = new Follower(followerActorContext);
+        followerActor.underlyingActor().setBehavior(follower);
+        followerActorContext.setCurrentBehavior(follower);
+
+        leader = new Leader(leaderActorContext);
+
+        AppendEntries appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        AppendEntriesReply appendEntriesReply = MessageCollectorActor.expectFirstMatching(leaderActor, AppendEntriesReply.class);
+
+        MessageCollectorActor.clearMessages(followerActor);
+        MessageCollectorActor.clearMessages(leaderActor);
+
+        // Verify initial AppendEntries sent with the leader's current commit index.
+        assertEquals("getLeaderCommit", leaderCommitIndex, appendEntries.getLeaderCommit());
+        assertEquals("Log entries size", 0, appendEntries.getEntries().size());
+        assertEquals("getPrevLogIndex", 0, appendEntries.getPrevLogIndex());
+
+        leaderActor.underlyingActor().setBehavior(leader);
+        leaderActorContext.setCurrentBehavior(leader);
+
+        leader.handleMessage(followerActor, appendEntriesReply);
+
+        MessageCollectorActor.expectMatching(leaderActor, AppendEntriesReply.class, 1);
+        appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        assertEquals("getLeaderCommit", leaderCommitIndex, appendEntries.getLeaderCommit());
+        assertEquals("getPrevLogIndex", -1, appendEntries.getPrevLogIndex());
+        assertEquals("Log entries size", 2, appendEntries.getEntries().size());
+
+        assertEquals("First entry index", 0, appendEntries.getEntries().get(0).getIndex());
+        assertEquals("First entry term", 2, appendEntries.getEntries().get(0).getTerm());
+        assertEquals("First entry data", leadersFirstLogEntry.getData(),
+                appendEntries.getEntries().get(0).getData());
+        assertEquals("Second entry index", 1, appendEntries.getEntries().get(1).getIndex());
+        assertEquals("Second entry term", 2, appendEntries.getEntries().get(1).getTerm());
+        assertEquals("Second entry data", leadersSecondLogEntry.getData(),
+                appendEntries.getEntries().get(1).getData());
+
+        FollowerLogInformation followerInfo = leader.getFollower(FOLLOWER_ID);
+        assertEquals("getNextIndex", 2, followerInfo.getNextIndex());
+
+        List<ApplyState> applyStateList = MessageCollectorActor.expectMatching(followerActor, ApplyState.class, 2);
+
+        ApplyState applyState = applyStateList.get(0);
+        assertEquals("Follower's first ApplyState index", 0, applyState.getReplicatedLogEntry().getIndex());
+        assertEquals("Follower's first ApplyState term", 2, applyState.getReplicatedLogEntry().getTerm());
+        assertEquals("Follower's first ApplyState data", leadersFirstLogEntry.getData(),
+                applyState.getReplicatedLogEntry().getData());
+
+        applyState = applyStateList.get(1);
+        assertEquals("Follower's second ApplyState index", 1, applyState.getReplicatedLogEntry().getIndex());
+        assertEquals("Follower's second ApplyState term", 2, applyState.getReplicatedLogEntry().getTerm());
+        assertEquals("Follower's second ApplyState data", leadersSecondLogEntry.getData(),
+                applyState.getReplicatedLogEntry().getData());
+
+        assertEquals("Follower's commit index", 1, followerActorContext.getCommitIndex());
+        assertEquals("Follower's lastIndex", 1, followerActorContext.getReplicatedLog().lastIndex());
+        assertEquals("Follower's lastTerm", 2, followerActorContext.getReplicatedLog().lastTerm());
+    }
+
+    @Test
+    public void testHandleAppendEntriesReplyWithNewerTerm(){
+        logStart("testHandleAppendEntriesReplyWithNewerTerm");
+
+        MockRaftActorContext leaderActorContext = createActorContext();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(10000, TimeUnit.SECONDS));
+
+        leaderActorContext.setReplicatedLog(
+                new MockRaftActorContext.MockReplicatedLogBuilder().createEntries(0, 2, 2).build());
+
+        leader = new Leader(leaderActorContext);
+        leaderActor.underlyingActor().setBehavior(leader);
+        leaderActor.tell(new AppendEntriesReply("foo", 20, false, 1000, 10, (short) 1), ActorRef.noSender());
+
+        AppendEntriesReply appendEntriesReply = MessageCollectorActor.expectFirstMatching(leaderActor, AppendEntriesReply.class);
+
+        assertEquals(false, appendEntriesReply.isSuccess());
+        assertEquals(RaftState.Follower, leaderActor.underlyingActor().getFirstBehaviorChange().state());
+
+        MessageCollectorActor.clearMessages(leaderActor);
+    }
 
-        assertEquals("getNextIndex", 10, followerInfo.getNextIndex());
+    @Test
+    public void testHandleAppendEntriesReplyWithNewerTermWhenElectionsAreDisabled(){
+        logStart("testHandleAppendEntriesReplyWithNewerTermWhenElectionsAreDisabled");
+
+        MockRaftActorContext leaderActorContext = createActorContext();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(10000, TimeUnit.SECONDS));
+
+        leaderActorContext.setReplicatedLog(
+                new MockRaftActorContext.MockReplicatedLogBuilder().createEntries(0, 2, 2).build());
+        leaderActorContext.setRaftPolicy(createRaftPolicy(false, false));
+
+        leader = new Leader(leaderActorContext);
+        leaderActor.underlyingActor().setBehavior(leader);
+        leaderActor.tell(new AppendEntriesReply("foo", 20, false, 1000, 10, (short) 1), ActorRef.noSender());
+
+        AppendEntriesReply appendEntriesReply = MessageCollectorActor.expectFirstMatching(leaderActor, AppendEntriesReply.class);
+
+        assertEquals(false, appendEntriesReply.isSuccess());
+        assertEquals(RaftState.Leader, leaderActor.underlyingActor().getFirstBehaviorChange().state());
+
+        MessageCollectorActor.clearMessages(leaderActor);
     }
 
     @Test
@@ -921,7 +1670,13 @@ public class LeaderTest extends AbstractLeaderTest {
 
         leader = new Leader(leaderActorContext);
 
-        AppendEntriesReply reply = new AppendEntriesReply(FOLLOWER_ID, 1, true, 2, 1);
+        FollowerLogInformation followerInfo = leader.getFollower(FOLLOWER_ID);
+
+        assertEquals(payloadVersion, leader.getLeaderPayloadVersion());
+        assertEquals(RaftVersions.HELIUM_VERSION, followerInfo.getRaftVersion());
+
+        short payloadVersion = 5;
+        AppendEntriesReply reply = new AppendEntriesReply(FOLLOWER_ID, 1, true, 2, 1, payloadVersion);
 
         RaftActorBehavior raftActorBehavior = leader.handleAppendEntriesReply(followerActor, reply);
 
@@ -929,12 +1684,12 @@ public class LeaderTest extends AbstractLeaderTest {
 
         assertEquals(2, leaderActorContext.getCommitIndex());
 
-        ApplyLogEntries applyLogEntries = MessageCollectorActor.expectFirstMatching(
-                leaderActor, ApplyLogEntries.class);
+        ApplyJournalEntries applyJournalEntries = MessageCollectorActor.expectFirstMatching(
+                leaderActor, ApplyJournalEntries.class);
 
         assertEquals(2, leaderActorContext.getLastApplied());
 
-        assertEquals(2, applyLogEntries.getToIndex());
+        assertEquals(2, applyJournalEntries.getToIndex());
 
         List<ApplyState> applyStateList = MessageCollectorActor.getAllMatching(leaderActor,
                 ApplyState.class);
@@ -944,6 +1699,11 @@ public class LeaderTest extends AbstractLeaderTest {
         ApplyState applyState = applyStateList.get(0);
 
         assertEquals(2, applyState.getReplicatedLogEntry().getIndex());
+
+        assertEquals(2, followerInfo.getMatchIndex());
+        assertEquals(3, followerInfo.getNextIndex());
+        assertEquals(payloadVersion, followerInfo.getPayloadVersion());
+        assertEquals(RaftVersions.CURRENT_VERSION, followerInfo.getRaftVersion());
     }
 
     @Test
@@ -954,7 +1714,7 @@ public class LeaderTest extends AbstractLeaderTest {
 
         leader = new Leader(leaderActorContext);
 
-        AppendEntriesReply reply = new AppendEntriesReply("unkown-follower", 1, false, 10, 1);
+        AppendEntriesReply reply = new AppendEntriesReply("unkown-follower", 1, false, 10, 1, (short)0);
 
         RaftActorBehavior raftActorBehavior = leader.handleAppendEntriesReply(followerActor, reply);
 
@@ -962,161 +1722,199 @@ public class LeaderTest extends AbstractLeaderTest {
     }
 
     @Test
-    public void testHandleRequestVoteReply(){
-        logStart("testHandleRequestVoteReply");
+    public void testFollowerCatchUpWithAppendEntriesMaxDataSizeExceeded() {
+        logStart("testFollowerCatchUpWithAppendEntriesMaxDataSizeExceeded");
 
-        MockRaftActorContext leaderActorContext = createActorContext();
+        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(1000, TimeUnit.SECONDS));
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setSnapshotChunkSize(2);
 
-        leader = new Leader(leaderActorContext);
+        leaderActorContext.setReplicatedLog(
+                new MockRaftActorContext.MockReplicatedLogBuilder().createEntries(0, 4, 1).build());
+        long leaderCommitIndex = 3;
+        leaderActorContext.setCommitIndex(leaderCommitIndex);
+        leaderActorContext.setLastApplied(leaderCommitIndex);
 
-        // Should be a no-op.
-        RaftActorBehavior raftActorBehavior = leader.handleRequestVoteReply(followerActor,
-                new RequestVoteReply(1, true));
+        ReplicatedLogEntry leadersFirstLogEntry = leaderActorContext.getReplicatedLog().get(0);
+        ReplicatedLogEntry leadersSecondLogEntry = leaderActorContext.getReplicatedLog().get(1);
+        ReplicatedLogEntry leadersThirdLogEntry = leaderActorContext.getReplicatedLog().get(2);
+        ReplicatedLogEntry leadersFourthLogEntry = leaderActorContext.getReplicatedLog().get(3);
 
-        assertEquals(RaftState.Leader, raftActorBehavior.state());
+        MockRaftActorContext followerActorContext = createFollowerActorContextWithLeader();
 
-        raftActorBehavior = leader.handleRequestVoteReply(followerActor, new RequestVoteReply(1, false));
+        followerActorContext.setReplicatedLog(new MockRaftActorContext.MockReplicatedLogBuilder().build());
+        followerActorContext.setCommitIndex(-1);
+        followerActorContext.setLastApplied(-1);
 
-        assertEquals(RaftState.Leader, raftActorBehavior.state());
-    }
+        Follower follower = new Follower(followerActorContext);
+        followerActor.underlyingActor().setBehavior(follower);
+        followerActorContext.setCurrentBehavior(follower);
 
-    @Test
-    public void testIsolatedLeaderCheckNoFollowers() {
-        logStart("testIsolatedLeaderCheckNoFollowers");
+        leader = new Leader(leaderActorContext);
 
-        MockRaftActorContext leaderActorContext = createActorContext();
+        AppendEntries appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        AppendEntriesReply appendEntriesReply = MessageCollectorActor.expectFirstMatching(leaderActor, AppendEntriesReply.class);
 
-        leader = new Leader(leaderActorContext);
-        RaftActorBehavior behavior = leader.handleMessage(leaderActor, new IsolatedLeaderCheck());
-        Assert.assertTrue(behavior instanceof Leader);
-    }
+        MessageCollectorActor.clearMessages(followerActor);
+        MessageCollectorActor.clearMessages(leaderActor);
 
-    @Test
-    public void testIsolatedLeaderCheckTwoFollowers() throws Exception {
-        logStart("testIsolatedLeaderCheckTwoFollowers");
+        // Verify initial AppendEntries sent with the leader's current commit index.
+        assertEquals("getLeaderCommit", leaderCommitIndex, appendEntries.getLeaderCommit());
+        assertEquals("Log entries size", 0, appendEntries.getEntries().size());
+        assertEquals("getPrevLogIndex", 2, appendEntries.getPrevLogIndex());
 
-        new JavaTestKit(getSystem()) {{
+        leaderActor.underlyingActor().setBehavior(leader);
+        leaderActorContext.setCurrentBehavior(leader);
 
-            ActorRef followerActor1 = getTestActor();
-            ActorRef followerActor2 = getTestActor();
+        leader.handleMessage(followerActor, appendEntriesReply);
 
-            MockRaftActorContext leaderActorContext = createActorContext();
+        List<AppendEntries> appendEntriesList = MessageCollectorActor.expectMatching(followerActor, AppendEntries.class, 2);
+        MessageCollectorActor.expectMatching(leaderActor, AppendEntriesReply.class, 2);
 
-            Map<String, String> peerAddresses = new HashMap<>();
-            peerAddresses.put("follower-1", followerActor1.path().toString());
-            peerAddresses.put("follower-2", followerActor2.path().toString());
+        appendEntries = appendEntriesList.get(0);
+        assertEquals("getLeaderCommit", leaderCommitIndex, appendEntries.getLeaderCommit());
+        assertEquals("getPrevLogIndex", -1, appendEntries.getPrevLogIndex());
+        assertEquals("Log entries size", 2, appendEntries.getEntries().size());
 
-            leaderActorContext.setPeerAddresses(peerAddresses);
+        assertEquals("First entry index", 0, appendEntries.getEntries().get(0).getIndex());
+        assertEquals("First entry data", leadersFirstLogEntry.getData(),
+                appendEntries.getEntries().get(0).getData());
+        assertEquals("Second entry index", 1, appendEntries.getEntries().get(1).getIndex());
+        assertEquals("Second entry data", leadersSecondLogEntry.getData(),
+                appendEntries.getEntries().get(1).getData());
 
-            leader = new Leader(leaderActorContext);
+        appendEntries = appendEntriesList.get(1);
+        assertEquals("getLeaderCommit", leaderCommitIndex, appendEntries.getLeaderCommit());
+        assertEquals("getPrevLogIndex", -1, appendEntries.getPrevLogIndex());
+        assertEquals("Log entries size", 2, appendEntries.getEntries().size());
 
-            leader.markFollowerActive("follower-1");
-            leader.markFollowerActive("follower-2");
-            RaftActorBehavior behavior = leader.handleMessage(leaderActor, new IsolatedLeaderCheck());
-            Assert.assertTrue("Behavior not instance of Leader when all followers are active",
-                behavior instanceof Leader);
+        assertEquals("First entry index", 2, appendEntries.getEntries().get(0).getIndex());
+        assertEquals("First entry data", leadersThirdLogEntry.getData(),
+                appendEntries.getEntries().get(0).getData());
+        assertEquals("Second entry index", 3, appendEntries.getEntries().get(1).getIndex());
+        assertEquals("Second entry data", leadersFourthLogEntry.getData(),
+                appendEntries.getEntries().get(1).getData());
 
-            // kill 1 follower and verify if that got killed
-            final JavaTestKit probe = new JavaTestKit(getSystem());
-            probe.watch(followerActor1);
-            followerActor1.tell(PoisonPill.getInstance(), ActorRef.noSender());
-            final Terminated termMsg1 = probe.expectMsgClass(Terminated.class);
-            assertEquals(termMsg1.getActor(), followerActor1);
-
-            leader.markFollowerInActive("follower-1");
-            leader.markFollowerActive("follower-2");
-            behavior = leader.handleMessage(leaderActor, new IsolatedLeaderCheck());
-            Assert.assertTrue("Behavior not instance of Leader when majority of followers are active",
-                behavior instanceof Leader);
+        FollowerLogInformation followerInfo = leader.getFollower(FOLLOWER_ID);
+        assertEquals("getNextIndex", 4, followerInfo.getNextIndex());
 
-            // kill 2nd follower and leader should change to Isolated leader
-            followerActor2.tell(PoisonPill.getInstance(), null);
-            probe.watch(followerActor2);
-            followerActor2.tell(PoisonPill.getInstance(), ActorRef.noSender());
-            final Terminated termMsg2 = probe.expectMsgClass(Terminated.class);
-            assertEquals(termMsg2.getActor(), followerActor2);
-
-            leader.markFollowerInActive("follower-2");
-            behavior = leader.handleMessage(leaderActor, new IsolatedLeaderCheck());
-            Assert.assertTrue("Behavior not instance of IsolatedLeader when majority followers are inactive",
-                behavior instanceof IsolatedLeader);
-        }};
-    }
+        MessageCollectorActor.expectMatching(followerActor, ApplyState.class, 4);
 
+        assertEquals("Follower's commit index", 3, followerActorContext.getCommitIndex());
+        assertEquals("Follower's lastIndex", 3, followerActorContext.getReplicatedLog().lastIndex());
+    }
 
     @Test
-    public void testAppendEntryCallAtEndofAppendEntryReply() throws Exception {
-        logStart("testAppendEntryCallAtEndofAppendEntryReply");
+    public void testHandleRequestVoteReply(){
+        logStart("testHandleRequestVoteReply");
 
-        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        MockRaftActorContext leaderActorContext = createActorContext();
 
-        DefaultConfigParamsImpl configParams = new DefaultConfigParamsImpl();
-        //configParams.setHeartBeatInterval(new FiniteDuration(9, TimeUnit.SECONDS));
-        configParams.setIsolatedLeaderCheckInterval(new FiniteDuration(10, TimeUnit.SECONDS));
+        leader = new Leader(leaderActorContext);
 
-        leaderActorContext.setConfigParams(configParams);
+        // Should be a no-op.
+        RaftActorBehavior raftActorBehavior = leader.handleRequestVoteReply(followerActor,
+                new RequestVoteReply(1, true));
 
-        MockRaftActorContext followerActorContext = createActorContext(FOLLOWER_ID, followerActor);
+        assertEquals(RaftState.Leader, raftActorBehavior.state());
 
-        followerActorContext.setConfigParams(configParams);
+        raftActorBehavior = leader.handleRequestVoteReply(followerActor, new RequestVoteReply(1, false));
 
-        Follower follower = new Follower(followerActorContext);
-        followerActor.underlyingActor().setBehavior(follower);
+        assertEquals(RaftState.Leader, raftActorBehavior.state());
+    }
 
-        leaderActorContext.getReplicatedLog().removeFrom(0);
-        leaderActorContext.setCommitIndex(-1);
-        leaderActorContext.setLastApplied(-1);
+    @Test
+    public void testIsolatedLeaderCheckNoFollowers() {
+        logStart("testIsolatedLeaderCheckNoFollowers");
 
-        followerActorContext.getReplicatedLog().removeFrom(0);
-        followerActorContext.setCommitIndex(-1);
-        followerActorContext.setLastApplied(-1);
+        MockRaftActorContext leaderActorContext = createActorContext();
 
         leader = new Leader(leaderActorContext);
+        RaftActorBehavior behavior = leader.handleMessage(leaderActor, Leader.ISOLATED_LEADER_CHECK);
+        assertTrue(behavior instanceof Leader);
+    }
 
-        AppendEntriesReply appendEntriesReply = MessageCollectorActor.expectFirstMatching(
-                leaderActor, AppendEntriesReply.class);
+    @Test
+    public void testIsolatedLeaderCheckNoVotingFollowers() {
+        logStart("testIsolatedLeaderCheckNoVotingFollowers");
 
-        leader.handleMessage(followerActor, appendEntriesReply);
+        MockRaftActorContext followerActorContext = createFollowerActorContextWithLeader();
+        Follower follower = new Follower(followerActorContext);
+        followerActor.underlyingActor().setBehavior(follower);
 
-        // Clear initial heartbeat messages
+        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(1000, TimeUnit.SECONDS));
+        leaderActorContext.getPeerInfo(FOLLOWER_ID).setVotingState(VotingState.NON_VOTING);
 
-        leaderActor.underlyingActor().clear();
-        followerActor.underlyingActor().clear();
+        leader = new Leader(leaderActorContext);
+        leader.getFollower(FOLLOWER_ID).markFollowerActive();
+        RaftActorBehavior behavior = leader.handleMessage(leaderActor, Leader.ISOLATED_LEADER_CHECK);
+        assertTrue("Expected Leader", behavior instanceof Leader);
+    }
 
-        // create 3 entries
-        leaderActorContext.setReplicatedLog(
-                new MockRaftActorContext.MockReplicatedLogBuilder().createEntries(0, 3, 1).build());
-        leaderActorContext.setCommitIndex(1);
-        leaderActorContext.setLastApplied(1);
+    private RaftActorBehavior setupIsolatedLeaderCheckTestWithTwoFollowers(RaftPolicy raftPolicy){
+        ActorRef followerActor1 = getSystem().actorOf(MessageCollectorActor.props(), "follower-1");
+        ActorRef followerActor2 = getSystem().actorOf(MessageCollectorActor.props(), "follower-2");
 
-        Uninterruptibles.sleepUninterruptibly(leaderActorContext.getConfigParams().getHeartBeatInterval().toMillis(),
-                TimeUnit.MILLISECONDS);
+        MockRaftActorContext leaderActorContext = createActorContext();
 
-        leader.handleMessage(leaderActor, new SendHeartBeat());
+        Map<String, String> peerAddresses = new HashMap<>();
+        peerAddresses.put("follower-1", followerActor1.path().toString());
+        peerAddresses.put("follower-2", followerActor2.path().toString());
 
-        AppendEntries appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        leaderActorContext.setPeerAddresses(peerAddresses);
+        leaderActorContext.setRaftPolicy(raftPolicy);
 
-        // Should send first log entry
-        assertEquals(1, appendEntries.getLeaderCommit());
-        assertEquals(0, appendEntries.getEntries().get(0).getIndex());
-        assertEquals(-1, appendEntries.getPrevLogIndex());
+        leader = new Leader(leaderActorContext);
 
-        appendEntriesReply = MessageCollectorActor.expectFirstMatching(leaderActor, AppendEntriesReply.class);
+        leader.markFollowerActive("follower-1");
+        leader.markFollowerActive("follower-2");
+        RaftActorBehavior behavior = leader.handleMessage(leaderActor, Leader.ISOLATED_LEADER_CHECK);
+        assertTrue("Behavior not instance of Leader when all followers are active", behavior instanceof Leader);
+
+        // kill 1 follower and verify if that got killed
+        final JavaTestKit probe = new JavaTestKit(getSystem());
+        probe.watch(followerActor1);
+        followerActor1.tell(PoisonPill.getInstance(), ActorRef.noSender());
+        final Terminated termMsg1 = probe.expectMsgClass(Terminated.class);
+        assertEquals(termMsg1.getActor(), followerActor1);
+
+        leader.markFollowerInActive("follower-1");
+        leader.markFollowerActive("follower-2");
+        behavior = leader.handleMessage(leaderActor, Leader.ISOLATED_LEADER_CHECK);
+        assertTrue("Behavior not instance of Leader when majority of followers are active", behavior instanceof Leader);
+
+        // kill 2nd follower and leader should change to Isolated leader
+        followerActor2.tell(PoisonPill.getInstance(), null);
+        probe.watch(followerActor2);
+        followerActor2.tell(PoisonPill.getInstance(), ActorRef.noSender());
+        final Terminated termMsg2 = probe.expectMsgClass(Terminated.class);
+        assertEquals(termMsg2.getActor(), followerActor2);
+
+        leader.markFollowerInActive("follower-2");
+        return leader.handleMessage(leaderActor, Leader.ISOLATED_LEADER_CHECK);
+    }
 
-        assertEquals(1, appendEntriesReply.getLogLastTerm());
-        assertEquals(0, appendEntriesReply.getLogLastIndex());
+    @Test
+    public void testIsolatedLeaderCheckTwoFollowers() throws Exception {
+        logStart("testIsolatedLeaderCheckTwoFollowers");
 
-        followerActor.underlyingActor().clear();
+        RaftActorBehavior behavior = setupIsolatedLeaderCheckTestWithTwoFollowers(DefaultRaftPolicy.INSTANCE);
 
-        leader.handleAppendEntriesReply(followerActor, appendEntriesReply);
+        assertTrue("Behavior not instance of IsolatedLeader when majority followers are inactive",
+            behavior instanceof IsolatedLeader);
+    }
 
-        appendEntries = MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+    @Test
+    public void testIsolatedLeaderCheckTwoFollowersWhenElectionsAreDisabled() throws Exception {
+        logStart("testIsolatedLeaderCheckTwoFollowersWhenElectionsAreDisabled");
 
-        // Should send second log entry
-        assertEquals(1, appendEntries.getLeaderCommit());
-        assertEquals(1, appendEntries.getEntries().get(0).getIndex());
+        RaftActorBehavior behavior = setupIsolatedLeaderCheckTestWithTwoFollowers(createRaftPolicy(false, true));
 
-        follower.close();
+        assertTrue("Behavior should not switch to IsolatedLeader because elections are disabled",
+                behavior instanceof Leader);
     }
 
     @Test
@@ -1159,7 +1957,7 @@ public class LeaderTest extends AbstractLeaderTest {
 
             for(int i=1;i<6;i++) {
                 // Each AppendEntriesReply could end up rescheduling the heartbeat (without the fix for bug 2733)
-                RaftActorBehavior newBehavior = leader.handleMessage(follower1Actor, new AppendEntriesReply(follower1ActorId, 1, true, i, 1));
+                RaftActorBehavior newBehavior = leader.handleMessage(follower1Actor, new AppendEntriesReply(follower1ActorId, 1, true, i, 1, (short)0));
                 assertTrue(newBehavior == leader);
                 Uninterruptibles.sleepUninterruptibly(200, TimeUnit.MILLISECONDS);
             }
@@ -1179,8 +1977,222 @@ public class LeaderTest extends AbstractLeaderTest {
         }};
     }
 
+    @Test
+    public void testReplicationConsensusWithNonVotingFollower() {
+        logStart("testReplicationConsensusWithNonVotingFollower");
+
+        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(1000, TimeUnit.SECONDS));
+
+        leaderActorContext.setReplicatedLog(new MockRaftActorContext.MockReplicatedLogBuilder().build());
+
+        String nonVotingFollowerId = "nonvoting-follower";
+        TestActorRef<ForwardMessageToBehaviorActor> nonVotingFollowerActor = actorFactory.createTestActor(
+                Props.create(MessageCollectorActor.class), actorFactory.generateActorId(nonVotingFollowerId));
+
+        leaderActorContext.addToPeers(nonVotingFollowerId, nonVotingFollowerActor.path().toString(), VotingState.NON_VOTING);
+
+        leader = new Leader(leaderActorContext);
+        leaderActorContext.setCurrentBehavior(leader);
+
+        // Ignore initial heartbeats
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        MessageCollectorActor.expectFirstMatching(nonVotingFollowerActor, AppendEntries.class);
+
+        MessageCollectorActor.clearMessages(followerActor);
+        MessageCollectorActor.clearMessages(nonVotingFollowerActor);
+        MessageCollectorActor.clearMessages(leaderActor);
+
+        // Send a Replicate message and wait for AppendEntries.
+        sendReplicate(leaderActorContext, 0);
+
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        MessageCollectorActor.expectFirstMatching(nonVotingFollowerActor, AppendEntries.class);
+
+        // Send reply only from the voting follower and verify consensus via ApplyState.
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, 0, 1, (short)0));
+
+        MessageCollectorActor.expectFirstMatching(leaderActor, ApplyState.class);
+
+        leader.handleMessage(leaderActor, new AppendEntriesReply(nonVotingFollowerId, 1, true, 0, 1, (short)0));
+
+        MessageCollectorActor.clearMessages(followerActor);
+        MessageCollectorActor.clearMessages(nonVotingFollowerActor);
+        MessageCollectorActor.clearMessages(leaderActor);
+
+        // Send another Replicate message
+        sendReplicate(leaderActorContext, 1);
+
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        AppendEntries appendEntries = MessageCollectorActor.expectFirstMatching(nonVotingFollowerActor,
+                AppendEntries.class);
+        assertEquals("Log entries size", 1, appendEntries.getEntries().size());
+        assertEquals("Log entry index", 1, appendEntries.getEntries().get(0).getIndex());
+
+        // Send reply only from the non-voting follower and verify no consensus via no ApplyState.
+        leader.handleMessage(leaderActor, new AppendEntriesReply(nonVotingFollowerId, 1, true, 1, 1, (short)0));
+
+        MessageCollectorActor.assertNoneMatching(leaderActor, ApplyState.class, 500);
+
+        // Send reply from the voting follower and verify consensus.
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, 1, 1, (short)0));
+
+        MessageCollectorActor.expectFirstMatching(leaderActor, ApplyState.class);
+    }
+
+    @Test
+    public void testTransferLeadershipWithFollowerInSync() {
+        logStart("testTransferLeadershipWithFollowerInSync");
+
+        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(1000, TimeUnit.SECONDS));
+        leaderActorContext.setReplicatedLog(new MockRaftActorContext.MockReplicatedLogBuilder().build());
+
+        leader = new Leader(leaderActorContext);
+        leaderActorContext.setCurrentBehavior(leader);
+
+        // Initial heartbeat
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, -1, -1, (short)0));
+        MessageCollectorActor.clearMessages(followerActor);
+
+        sendReplicate(leaderActorContext, 0);
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, 0, 1, (short)0));
+        MessageCollectorActor.expectFirstMatching(leaderActor, ApplyState.class);
+        MessageCollectorActor.clearMessages(followerActor);
+
+        RaftActorLeadershipTransferCohort mockTransferCohort = mock(RaftActorLeadershipTransferCohort.class);
+        leader.transferLeadership(mockTransferCohort);
+
+        verify(mockTransferCohort, never()).transferComplete();
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, 0, 1, (short)0));
+
+        // Expect a final AppendEntries to ensure the follower's lastApplied index is up-to-date
+        MessageCollectorActor.expectMatching(followerActor, AppendEntries.class, 2);
+
+        // Leader should force an election timeout
+        MessageCollectorActor.expectFirstMatching(followerActor, ElectionTimeout.class);
+
+        verify(mockTransferCohort).transferComplete();
+    }
+
+    @Test
+    public void testTransferLeadershipWithEmptyLog() {
+        logStart("testTransferLeadershipWithEmptyLog");
+
+        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(1000, TimeUnit.SECONDS));
+        leaderActorContext.setReplicatedLog(new MockRaftActorContext.MockReplicatedLogBuilder().build());
+
+        leader = new Leader(leaderActorContext);
+        leaderActorContext.setCurrentBehavior(leader);
+
+        // Initial heartbeat
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, -1, -1, (short)0));
+        MessageCollectorActor.clearMessages(followerActor);
+
+        RaftActorLeadershipTransferCohort mockTransferCohort = mock(RaftActorLeadershipTransferCohort.class);
+        leader.transferLeadership(mockTransferCohort);
+
+        verify(mockTransferCohort, never()).transferComplete();
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, -1, -1, (short)0));
+
+        // Expect a final AppendEntries to ensure the follower's lastApplied index is up-to-date
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        // Leader should force an election timeout
+        MessageCollectorActor.expectFirstMatching(followerActor, ElectionTimeout.class);
+
+        verify(mockTransferCohort).transferComplete();
+    }
+
+    @Test
+    public void testTransferLeadershipWithFollowerInitiallyOutOfSync() {
+        logStart("testTransferLeadershipWithFollowerInitiallyOutOfSync");
+
+        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(200, TimeUnit.MILLISECONDS));
+
+        leader = new Leader(leaderActorContext);
+        leaderActorContext.setCurrentBehavior(leader);
+
+        // Initial heartbeat
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        MessageCollectorActor.clearMessages(followerActor);
+
+        RaftActorLeadershipTransferCohort mockTransferCohort = mock(RaftActorLeadershipTransferCohort.class);
+        leader.transferLeadership(mockTransferCohort);
+
+        verify(mockTransferCohort, never()).transferComplete();
+
+        // Sync up the follower.
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, -1, -1, (short)0));
+        MessageCollectorActor.clearMessages(followerActor);
+
+        Uninterruptibles.sleepUninterruptibly(leaderActorContext.getConfigParams().
+                getHeartBeatInterval().toMillis() + 1, TimeUnit.MILLISECONDS);
+        leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, 1, 1, (short)0));
+
+        // Leader should force an election timeout
+        MessageCollectorActor.expectFirstMatching(followerActor, ElectionTimeout.class);
+
+        verify(mockTransferCohort).transferComplete();
+    }
+
+    @Test
+    public void testTransferLeadershipWithFollowerSyncTimeout() {
+        logStart("testTransferLeadershipWithFollowerSyncTimeout");
+
+        MockRaftActorContext leaderActorContext = createActorContextWithFollower();
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setHeartBeatInterval(
+                new FiniteDuration(200, TimeUnit.MILLISECONDS));
+        ((DefaultConfigParamsImpl)leaderActorContext.getConfigParams()).setElectionTimeoutFactor(2);
+        leaderActorContext.setReplicatedLog(new MockRaftActorContext.MockReplicatedLogBuilder().build());
+
+        leader = new Leader(leaderActorContext);
+        leaderActorContext.setCurrentBehavior(leader);
+
+        // Initial heartbeat
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+        leader.handleMessage(leaderActor, new AppendEntriesReply(FOLLOWER_ID, 1, true, -1, -1, (short)0));
+        MessageCollectorActor.clearMessages(followerActor);
+
+        sendReplicate(leaderActorContext, 0);
+        MessageCollectorActor.expectFirstMatching(followerActor, AppendEntries.class);
+
+        MessageCollectorActor.clearMessages(followerActor);
+
+        RaftActorLeadershipTransferCohort mockTransferCohort = mock(RaftActorLeadershipTransferCohort.class);
+        leader.transferLeadership(mockTransferCohort);
+
+        verify(mockTransferCohort, never()).transferComplete();
+
+        // Send heartbeats to time out the transfer.
+        for(int i = 0; i < leaderActorContext.getConfigParams().getElectionTimeoutFactor(); i++) {
+            Uninterruptibles.sleepUninterruptibly(leaderActorContext.getConfigParams().
+                    getHeartBeatInterval().toMillis() + 1, TimeUnit.MILLISECONDS);
+            leader.handleMessage(leaderActor, SendHeartBeat.INSTANCE);
+        }
+
+        verify(mockTransferCohort).abortTransfer();
+        verify(mockTransferCohort, never()).transferComplete();
+        MessageCollectorActor.assertNoneMatching(followerActor, ElectionTimeout.class, 100);
+    }
+
     @Override
-    protected void assertStateChangesToFollowerWhenRaftRPCHasNewerTerm(RaftActorContext actorContext,
+    protected void assertStateChangesToFollowerWhenRaftRPCHasNewerTerm(MockRaftActorContext actorContext,
             ActorRef actorRef, RaftRPC rpc) throws Exception {
         super.assertStateChangesToFollowerWhenRaftRPCHasNewerTerm(actorContext, actorRef, rpc);
         assertEquals("New votedFor", null, actorContext.getTermInformation().getVotedFor());