diff --git a/MVM.cabal b/MVM.cabal
index 33af7de..546c1d9 100644
--- a/MVM.cabal
+++ b/MVM.cabal
@@ -57,6 +57,7 @@ test-suite spec
   other-modules:      
       Assembler.TokenizerSpec  
       Assembler.ParserSpec
+      UtilSpec
 
       VirtualMachine
       Assembler.Tokenizer
diff --git a/app/Assembler/Tokenizer.hs b/app/Assembler/Tokenizer.hs
index c5a78cd..8612a40 100644
--- a/app/Assembler/Tokenizer.hs
+++ b/app/Assembler/Tokenizer.hs
@@ -111,12 +111,7 @@ sepTokenizer _ _ [] = Nothing
 sepTokenizer predicate tokenizer input = do
   result@(TokenizeResult _ consumed) <- tokenizer input
   let next = drop consumed input
-  let (isSep, _) =  if null next 
-                           then (True, 0)
-                           else if predicate . head $ next
-                             then (True, 1)
-                             else (False, 0)
-  if isSep
+  if null next || (predicate . head $ next)
   then return $ result
   else Nothing
 
diff --git a/app/Util.hs b/app/Util.hs
index ed0138c..ea8feb1 100644
--- a/app/Util.hs
+++ b/app/Util.hs
@@ -63,6 +63,7 @@ controlChar x = case x of
 explode :: (Foldable f) => (a -> Bool) -> f a -> [[a]]
 explode predicate xs = filter (not . null) $ foldr split [[]] xs 
   where 
+    split _ [] = []
     split y (ys:yss) 
       | predicate y = []:ys:yss
-      | otherwise   = (y:ys):yss
\ No newline at end of file
+      | otherwise   = (y:ys):yss    
\ No newline at end of file
diff --git a/app/VirtualMachine.hs b/app/VirtualMachine.hs
index eba5890..3ea4736 100644
--- a/app/VirtualMachine.hs
+++ b/app/VirtualMachine.hs
@@ -97,6 +97,8 @@ instructions = [ Simple  { _op = Nop,  _noParams = 0, _noPops = 0, _sAction = (\
                ]
 
 jumpIf :: (Int -> Int -> Bool) -> VM -> Args -> Either String VM
+jumpIf _ _ [] = Left $ "Address expected"
+jumpIf _ _ (_:_:_) = Left $ "Multiple parameters are not supported by jmp* instructions"
 jumpIf predicate vm [addr] = Right $ vm { _pc = pc }
   where
     (top:_) = toList . _stack $ vm
diff --git a/test/UtilSpec.hs b/test/UtilSpec.hs
new file mode 100644
index 0000000..dedb14f
--- /dev/null
+++ b/test/UtilSpec.hs
@@ -0,0 +1,63 @@
+module UtilSpec where
+
+import Prelude hiding (head)
+import Test.Hspec
+import Util
+
+import Data.Word
+import Data.Char (chr)
+
+spec :: Spec
+spec = do
+  describe "toLowerCase" $ do
+    it "converts arbitrary string to lowercase" $
+      toLowerCase "Some UpPeR CASED sTRi_NG" `shouldBe` "some upper cased stri_ng"
+    it "does not convert already lowercased string" $
+      toLowerCase "some lower cased string" `shouldBe` "some lower cased string"
+  
+  describe "byteStr" $ do
+    it "presents byte as hex" $ do
+      let input    = [0,    1,    5,    10,   15,   16,   255 ] :: [Word8]
+      let expected = ["00", "01", "05", "0a", "0f", "10", "ff"]
+      map byteStr input `shouldBe` expected
+
+  describe "bytesStr" $ do
+    it "presents bytes as hex in fixed columns of width 5" $ do
+      let input    = [0..19] :: [Word8]
+      let expected = "00 01 02 03 04 \n\
+                     \05 06 07 08 09 \n\
+                     \0a 0b 0c 0d 0e \n\
+                     \0f 10 11 12 13"                
+      bytesStr 5 input `shouldBe` expected
+
+  describe "head" $ do
+    it "returns just a head of list" $ do
+      head [4, 3, 6] `shouldBe` (Just 4 :: Maybe Int)
+    it "returns Nothing if list is empty" $ do
+      head [] `shouldBe` (Nothing :: Maybe Int)
+
+  describe "unescape" $ do
+    it "properly converts escape sequences to correct ASCII characters" $ do
+      let input = "\\tHello,\\nworld!\\0"
+      let expected = "\tHello,\nworld!\0"
+      unescape input `shouldBe` Just expected
+    it "supports all escape sequences" $ do
+      let input = "\\n\\t\\v\\b\\r\\f\\a\\\\\\\"\\0"
+      let expected = map chr [10, 9, 11, 8, 13, 12, 7, 92, 34, 0]
+      unescape input `shouldBe` Just expected
+    it "returns nothing if unknown escape sequence encountered" $ do
+      let input = "Unknown escape: \\x"
+      unescape input `shouldBe` Nothing
+  
+  describe "explode" $ do
+    it "splits the list by given character" $ do
+      let input = "hello:world: what's : up?"
+      let expected = ["hello", "world", " what's ", " up?"]
+      explode (==':') input `shouldBe` expected
+    it "supports empty input" $ do
+      let input = ""      
+      explode (==':') input `shouldBe` []
+    it "filters out empty lists" $ do
+      let input = ":hello:world:::::: what's : up?"
+      let expected = ["hello", "world", " what's ", " up?"]
+      explode (==':') input `shouldBe` expected
\ No newline at end of file