diff --git a/src/main/scala/com/fluency03/blockchain/api/actors/BlockchainActor.scala b/src/main/scala/com/fluency03/blockchain/api/actors/BlockchainActor.scala
index 08c77f9..4a6c11f 100644
--- a/src/main/scala/com/fluency03/blockchain/api/actors/BlockchainActor.scala
+++ b/src/main/scala/com/fluency03/blockchain/api/actors/BlockchainActor.scala
@@ -48,14 +48,14 @@ class BlockchainActor extends ActorSupport {
 
   /**
    * TODO (Chang): new APIS:
-   *  - MineNextBlock
-   *
+   *  - AddBlock with Block obtained from pool based on hash
+   *  - MineNextBlock with Transactions
    */
 
   private def onGetBlockchain(): Unit = sender() ! blockchainOpt
 
   private def onCreateBlockchain(): Unit =
-    if (blockchainOpt.isDefined) sender() ! FailureMsg(s"Blockchain already exists.")
+    if (blockchainOpt.isDefined) sender() ! FailureMsg("Blockchain already exists.")
     else {
       blockchainOpt = Some(Blockchain())
       if (hashIndexMapping.nonEmpty) {
@@ -70,8 +70,8 @@ class BlockchainActor extends ActorSupport {
     if (blockchainOpt.isDefined) {
       blockchainOpt = None
       hashIndexMapping.clear()
-      sender() ! SuccessMsg(s"Blockchain deleted.")
-    } else sender() ! FailureMsg(s"Blockchain does not exist.")
+      sender() ! SuccessMsg("Blockchain deleted.")
+    } else sender() ! FailureMsg("Blockchain does not exist.")
 
   private def onGetBlock(hash: String): Unit = sender() ! getBlock(hash)
 
@@ -86,11 +86,11 @@ class BlockchainActor extends ActorSupport {
     case Some(blockchain) =>
       blockchainOpt = Some(blockchain.addBlock(block))
       hashIndexMapping += (block.hash -> blockchain.length)
-      sender() ! SuccessMsg(s"New Block added on the chain.")
+      sender() ! SuccessMsg(s"New Block ${block.hash} added on the chain.")
     case None =>
       log.error("Blockchain does not exist! Clear the hash-to-index mapping!")
       hashIndexMapping.clear()
-      sender() ! FailureMsg(s"Blockchain does not exist.")
+      sender() ! FailureMsg("Blockchain does not exist.")
   }
 
   private def onRemoveBlock(): Unit = blockchainOpt match {
@@ -98,11 +98,11 @@ class BlockchainActor extends ActorSupport {
       val toBeRemoved = blockchain.chain.head
       blockchainOpt = Some(blockchain.removeBlock())
       hashIndexMapping -= toBeRemoved.hash
-      sender() ! SuccessMsg(s"Last Block removed from the chain.")
+      sender() ! SuccessMsg(s"Last Block ${toBeRemoved.hash} removed from the chain.")
     case None =>
       log.error("Blockchain does not exist! Clear the hash-to-index mapping!")
       hashIndexMapping.clear()
-      sender() ! FailureMsg(s"Blockchain does not exist.")
+      sender() ! FailureMsg("Blockchain does not exist.")
   }
 
   private def onMineNextBlock(data: String, trans: Seq[Transaction]): Unit = blockchainOpt match {
@@ -120,7 +120,7 @@ class BlockchainActor extends ActorSupport {
     case None =>
       log.error("Blockchain does not exist! Clear the hash-to-index mapping!")
       hashIndexMapping.clear()
-      sender() ! FailureMsg(s"Blockchain does not exist.")
+      sender() ! FailureMsg("Blockchain does not exist.")
   }
 
 
diff --git a/src/main/scala/com/fluency03/blockchain/api/routes/BlockchainRoutes.scala b/src/main/scala/com/fluency03/blockchain/api/routes/BlockchainRoutes.scala
index aff40cc..02d2ab1 100644
--- a/src/main/scala/com/fluency03/blockchain/api/routes/BlockchainRoutes.scala
+++ b/src/main/scala/com/fluency03/blockchain/api/routes/BlockchainRoutes.scala
@@ -21,8 +21,8 @@ trait BlockchainRoutes extends RoutesSupport {
 
   /**
    * TODO (Chang): new APIS:
-   *  - MineNextBlock
-   *
+   *  - AddBlock with Block obtained from pool based on hash
+   *  - MineNextBlock with Transactions
    */
 
   lazy val blockchainRoutes: Route =
diff --git a/src/main/scala/com/fluency03/blockchain/core/Blockchain.scala b/src/main/scala/com/fluency03/blockchain/core/Blockchain.scala
index 2b4e0ee..6c88ee6 100644
--- a/src/main/scala/com/fluency03/blockchain/core/Blockchain.scala
+++ b/src/main/scala/com/fluency03/blockchain/core/Blockchain.scala
@@ -50,6 +50,7 @@ object Blockchain {
 
   def apply(difficulty: Int): Blockchain = new Blockchain(difficulty, Seq(Block.genesis(difficulty)))
 
+  // TODO (Chang): return both the validity and highest valid Block index
   @tailrec
   def isValidChain(chain: Seq[Block]): Boolean = chain match {
     case Nil => true
diff --git a/src/test/scala/com/fluency03/blockchain/api/actors/BlockchainActorTest.scala b/src/test/scala/com/fluency03/blockchain/api/actors/BlockchainActorTest.scala
index 7c2c2ce..a29bb38 100644
--- a/src/test/scala/com/fluency03/blockchain/api/actors/BlockchainActorTest.scala
+++ b/src/test/scala/com/fluency03/blockchain/api/actors/BlockchainActorTest.scala
@@ -4,7 +4,7 @@ import akka.actor.{ActorRef, ActorSystem, Props}
 import akka.testkit.{DefaultTimeout, ImplicitSender, TestKit}
 import com.fluency03.blockchain.api.actors.BlockchainActor._
 import com.fluency03.blockchain.api.{FailureMsg, SuccessMsg}
-import com.fluency03.blockchain.core.{Block, Blockchain}
+import com.fluency03.blockchain.core.{Block, Blockchain, Transaction}
 import org.scalatest.{BeforeAndAfterAll, Matchers, WordSpecLike}
 
 import scala.concurrent.duration._
@@ -52,11 +52,47 @@ class BlockchainActorTest extends TestKit(ActorSystem("BlockchainActorTest")) wi
       blockchainActor ! GetTxOfBlock(genesis.transactions.head.id, "bb")
       expectMsg(None)
 
+      blockchainActor ! CheckBlockchainValidity
+      expectMsg(SuccessMsg("true"))
+
+      blockchainActor ! AddBlock(genesis)
+      expectMsg(SuccessMsg(s"New Block ${genesis.hash} added on the chain."))
+
+      blockchainActor ! CheckBlockchainValidity
+      expectMsg(SuccessMsg("false"))
+
+      blockchainActor ! RemoveBlock
+      expectMsg(SuccessMsg(s"Last Block ${genesis.hash} removed from the chain."))
+
+      blockchainActor ! CheckBlockchainValidity
+      expectMsg(SuccessMsg("true"))
+
+      blockchainActor ! MineNextBlock("next", Seq.empty[Transaction])
+      val actualBlock = expectMsgType[Some[Block]].get
+      actualBlock.data shouldEqual "next"
+      actualBlock.transactions shouldEqual Seq.empty[Transaction]
+      actualBlock.difficulty shouldEqual blockchain.difficulty
+      actualBlock.index shouldEqual 1
+      actualBlock.hasValidHash shouldEqual true
+      actualBlock.previousHash shouldEqual genesis.hash
+
       blockchainActor ! DeleteBlockchain
-      expectMsg(SuccessMsg(s"Blockchain deleted."))
+      expectMsg(SuccessMsg("Blockchain deleted."))
 
       blockchainActor ! DeleteBlockchain
-      expectMsg(FailureMsg(s"Blockchain does not exist."))
+      expectMsg(FailureMsg("Blockchain does not exist."))
+
+      blockchainActor ! AddBlock(genesis)
+      expectMsg(FailureMsg("Blockchain does not exist."))
+
+      blockchainActor ! RemoveBlock
+      expectMsg(FailureMsg("Blockchain does not exist."))
+
+      blockchainActor ! CheckBlockchainValidity
+      expectMsg(FailureMsg("Blockchain does not exist."))
+
+      blockchainActor ! MineNextBlock("next", Seq.empty[Transaction])
+      expectMsg(None)
 
       blockchainActor ! "other"
       expectNoMessage