diff --git a/LambdaDB.cabal b/LambdaDB.cabal
--- a/LambdaDB.cabal
+++ b/LambdaDB.cabal
@@ -1,47 +1,48 @@
-name:                LambdaDB
-version:             0.0.0.5
-synopsis:            On-memory Database using Lambda Function environment.
-description:         Please see README.md
-homepage:            https://github.com/ailrun/LambdaDB/blob/master/README.md
-license:             BSD3
-license-file:        LICENSE
-author:              Junyoung Clare Jang
-maintainer:          jjc9310@gmail.com
-copyright:           2016 Junyoung Clare Jang
-category:            Database
-build-type:          Simple
--- extra-source-files:
-cabal-version:       >=1.10
-
-library
-  hs-source-dirs:      src
-  exposed-modules:     Lib
-                     , Database.LambdaDB
-                     , Database.LambdaDB.Command
-                     , Database.LambdaDB.DBType
-                     , Database.LambdaDB.DataType
-  build-depends:       base >= 4.7 && < 5
-                     , containers
-                     , transformers
-  default-language:    Haskell2010
-
-executable LambdaDB-exe
-  hs-source-dirs:      app
-  main-is:             Main.hs
-  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
-  build-depends:       base
-                     , LambdaDB
-  default-language:    Haskell2010
-
-test-suite LambdaDB-test
-  type:                exitcode-stdio-1.0
-  hs-source-dirs:      test
-  main-is:             Spec.hs
-  build-depends:       base
-                     , LambdaDB
-  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
-  default-language:    Haskell2010
-
-source-repository head
-  type:     git
-  location: https://github.com/ailrun/LambdaDB
+name:                LambdaDB
+version:             0.0.0.6
+synopsis:            On-memory Database using Lambda Function environment.
+description:         Please see README.md
+homepage:            https://github.com/ailrun/LambdaDB/blob/master/README.md
+license:             BSD3
+license-file:        LICENSE
+author:              Junyoung Clare Jang
+maintainer:          jjc9310@gmail.com
+copyright:           2016 Junyoung Clare Jang
+category:            Database
+build-type:          Simple
+-- extra-source-files:
+cabal-version:       >=1.10
+
+library
+  hs-source-dirs:      src
+  exposed-modules:     Lib
+                     , Database.LambdaDB
+                     , Database.LambdaDB.Command
+                     , Database.LambdaDB.DBType
+                     , Database.LambdaDB.DataType
+  build-depends:       base >= 4.7 && < 5
+                     , containers
+                     , transformers
+  default-language:    Haskell2010
+
+executable LambdaDB-exe
+  hs-source-dirs:      app
+  main-is:             Main.hs
+  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
+  build-depends:       base
+                     , LambdaDB
+  default-language:    Haskell2010
+
+test-suite LambdaDB-test
+  type:                exitcode-stdio-1.0
+  hs-source-dirs:      test
+  main-is:             Spec.hs
+  build-depends:       base
+                     , QuickCheck
+                     , LambdaDB
+  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
+  default-language:    Haskell2010
+
+source-repository head
+  type:     git
+  location: https://github.com/ailrun/LambdaDB
diff --git a/src/Database/LambdaDB.hs b/src/Database/LambdaDB.hs
--- a/src/Database/LambdaDB.hs
+++ b/src/Database/LambdaDB.hs
@@ -2,6 +2,7 @@
   ( Command(..),
     DB(..),
     DBData(..),
+    None(..),
     Key,
     initDB,
     insertData,
diff --git a/src/Database/LambdaDB/Command.hs b/src/Database/LambdaDB/Command.hs
--- a/src/Database/LambdaDB/Command.hs
+++ b/src/Database/LambdaDB/Command.hs
@@ -6,10 +6,10 @@
 
 import Database.LambdaDB.DataType
 
-data Command = ComError
-             | ComQuit
+data Command = ComQuit
              | ComStatus
              | ComInsert Key DBData
+             | ComDelete Key
              | ComFind Key
              deriving (Show)
 
@@ -19,20 +19,22 @@
     (\x -> [(ComQuit, t) |
             (s, t) <- lex x,
             "quit" <- [map toLower s]]) r
-    ++
-    readParen (d > app_prec)
+    ++ readParen (d > app_prec)
     (\x -> [(ComStatus, t) |
             (s, t) <- lex x,
             "status" <- [map toLower s]]) r
-    ++
-    readParen (d > app_prec)
+    ++ readParen (d > app_prec)
     (\x -> [(ComInsert k v, w) |
             (s, t) <- lex x,
             "insert" <- [map toLower s],
             (k, u) <- lex t,
             (v, w) <- readsPrec 0 u]) r
-    ++
-    readParen (d > app_prec)
+    ++ readParen (d > app_prec)
+    (\x -> [(ComDelete k, u) |
+            (s, t) <- lex x,
+            "delete" <- [map toLower s],
+            (k, u) <- lex t]) r
+    ++ readParen (d > app_prec)
     (\x -> [(ComFind k, u) |
              (s, t) <- lex x,
              "find" <- [map toLower s],
diff --git a/src/Database/LambdaDB/DBType.hs b/src/Database/LambdaDB/DBType.hs
--- a/src/Database/LambdaDB/DBType.hs
+++ b/src/Database/LambdaDB/DBType.hs
@@ -20,7 +20,7 @@
                           $ \x -> if (x == key) then
                                     value
                                   else
-                                    unLambda db key
+                                    unLambda db x
 
 findData :: Key -> DB -> DBData
 findData key db = unLambda db key
diff --git a/src/Database/LambdaDB/DataType.hs b/src/Database/LambdaDB/DataType.hs
--- a/src/Database/LambdaDB/DataType.hs
+++ b/src/Database/LambdaDB/DataType.hs
@@ -50,6 +50,7 @@
     DBNone None -> showString "None"
     DBBool b -> showsPrec d b
     DBChar c -> showsPrec d c
+    DBString s -> showString s
     DBInt i -> showsPrec d i
     DBInteger ii -> showParen (d > app_prec)
                     $ showsPrec (app_prec+1) ii . showString "i"
diff --git a/src/Lib.hs b/src/Lib.hs
--- a/src/Lib.hs
+++ b/src/Lib.hs
@@ -1,57 +1,60 @@
-module Lib
-  ( dbInit,
-    dbProc,
-    dbTerm
-  ) where
-
--- Standard libraries
-import Data.Data
-
-import Control.Monad
-import Control.Monad.Trans.Class
-import Control.Monad.Trans.Maybe
-
--- Custom libraries
-import Database.LambdaDB
-
-dbInit :: IO DB
-dbInit = do
-  putStrLn "Initiate DB ..."
-  return initDB
-
-dbProc :: DB -> IO ()
-dbProc d = void . runMaybeT $ do
-  lift . putStrLn $ "DB is now running"
-  void . g $ d
-  return ()
-  where g db = do
-          com <- lift getLine
-          newdb <- case com of
-                  "" -> lift . return $ db
-                  _ ->
-                    case (read com) of
-                      ComQuit -> mzero
-                      ComStatus -> lift . dbStatus $ db
-                      ComInsert k v -> lift . dbInsert k v $ db
-                      ComFind k -> lift . dbFind k $ db
-                      _ -> do
-                        lift . putStrLn $ "Command Error"
-                        return db
-          g newdb
-
-dbStatus :: DB -> IO DB
-dbStatus db = do
-  putStrLn "On running"
-  return db
-
-dbInsert :: Key -> DBData -> DB -> IO DB
-dbInsert k v db = do
-  return . insertData k v $ db
-
-dbFind :: Key -> DB -> IO DB
-dbFind k db = do
-  putStrLn . show . findData k $ db
-  return db
-
-dbTerm :: IO ()
-dbTerm = putStrLn "Terminate DB"
+module Lib
+  ( dbInit,
+    dbProc,
+    dbTerm
+  ) where
+
+-- Standard libraries
+import Control.Monad
+import Control.Monad.Trans.Class
+import Control.Monad.Trans.Maybe
+
+-- Custom libraries
+import Database.LambdaDB
+
+dbInit :: IO DB
+dbInit = do
+  putStrLn "Initiate DB ..."
+  return initDB
+
+dbProc :: DB -> IO ()
+dbProc d = void . runMaybeT $ do
+  lift . putStrLn $ "DB is now running"
+  void . g $ d
+  return ()
+  where g db = do
+          com <- lift getLine
+          newdb <- case com of
+                  "" -> lift . return $ db
+                  _ ->
+                    case (readsPrec 0 com) of
+                      (ComQuit, _):_ -> mzero
+                      (ComStatus, _):_ -> lift . dbStatus $ db
+                      (ComInsert k v, _):_ -> lift . dbInsert k v $ db
+                      (ComDelete k, _):_ -> do
+                        lift. print $ k
+                        lift. dbInsert k (DBNone None) $ db
+                      (ComFind k, _):_ -> lift . dbFind k $ db
+                      _ -> do
+                        lift . putStrLn $ "Command Error"
+                        return db
+          g newdb
+
+dbStatus :: DB -> IO DB
+dbStatus db = do
+  putStrLn "On running"
+  return db
+
+dbInsert :: Key -> DBData -> DB -> IO DB
+dbInsert k v db = do
+  let newdb = insertData k v db
+  putStrLn "OK"
+  return newdb
+
+dbFind :: Key -> DB -> IO DB
+dbFind k db = do
+  putStrLn . show . findData k $ db
+  return db
+
+dbTerm :: IO ()
+dbTerm = putStrLn "Terminate DB"
diff --git a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -1,2 +1,40 @@
-main :: IO ()
-main = putStrLn "Test suite not yet implemented"
+import Control.Monad
+
+import Test.QuickCheck
+import Database.LambdaDB
+
+instance Arbitrary DBData where
+  arbitrary = oneof [ liftM DBNone (return None),
+                      liftM DBBool arbitrary,
+                      liftM DBChar arbitrary,
+                      liftM DBString arbitrary,
+                      liftM DBInt arbitrary,
+                      liftM DBInteger arbitrary,
+                      liftM DBList (sized list')]
+    where list' n = list'' 5 n
+          list'' 0 _ = return []
+          list'' _ 0 = return []
+          list'' n m = (:) <$> oneof [ liftM DBNone (return None),
+                                    liftM DBBool arbitrary,
+                                    liftM DBChar arbitrary,
+                                    liftM DBString arbitrary,
+                                    liftM DBInt arbitrary,
+                                    liftM DBInteger arbitrary,
+                                    liftM DBList (list'' n (m-1))] <*> list'' (n-1) m
+
+ruleInsertFind :: Key -> [DBData] -> Bool
+ruleInsertFind k vs =
+  let ruleHelper key [] db = (findData key db) == DBNone None
+      ruleHelper key (x:[]) db =
+        let dbn = insertData key x db
+            xFind = (findData key dbn)
+        in xFind == x
+      ruleHelper key (x:xs) db =
+        let dbn = insertData key x db
+            xFind = (findData key dbn)
+        in xFind == x && ruleHelper key xs dbn
+  in
+    ruleHelper k vs initDB
+
+main :: IO ()
+main = quickCheck ruleInsertFind