diff --git a/common/TestUtil.hs b/common/TestUtil.hs
index 20b3c3d..832cf5a 100644
--- a/common/TestUtil.hs
+++ b/common/TestUtil.hs
@@ -118,6 +118,17 @@ intLiteral n = A.Literal emptyMeta A.Int $ A.IntLiteral emptyMeta (show n)
 intLiteralPattern :: Integer -> Pattern
 intLiteralPattern = (stopCaringPattern emptyMeta) . mkPattern . intLiteral
 
+
+-- | Creates an integer literal 'A.Expression' with the given integer.
+int64Literal :: Integer -> A.Expression
+int64Literal n = A.Literal emptyMeta A.Int64 $ A.IntLiteral emptyMeta (show n)
+
+-- | Creates a 'Pattern' to match an 'A.Expression' instance.
+-- @'assertPatternMatch' ('intLiteralPattern' x) ('intLiteral' x)@ will always succeed.
+-- All meta tags are ignored.
+int64LiteralPattern :: Integer -> Pattern
+int64LiteralPattern = (stopCaringPattern emptyMeta) . mkPattern . int64Literal
+
 -- | Creates a pair of variable lists, given a pair of variable-name lists as input.
 makeNamesWR :: ([String],[String]) -> ([A.Variable],[A.Variable])
 makeNamesWR (x,y) = (map variable x,map variable y)
diff --git a/frontends/RainTypesTest.hs b/frontends/RainTypesTest.hs
index f521033..9ffc38b 100644
--- a/frontends/RainTypesTest.hs
+++ b/frontends/RainTypesTest.hs
@@ -18,16 +18,39 @@ with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 module RainTypesTest where
 
-import Test.HUnit
+import Test.HUnit hiding (State)
 import TestUtil
 import RainTypes
 import TreeUtil
+import qualified AST as A
+import CompState
+import Control.Monad.State
 
 constantFoldTest :: Test
 constantFoldTest = TestList
  [
-  TestCase $ assertPatternMatch "constantFoldTest 0" (buildExprPattern $ Var "x") (buildExpr $ Var "x")
+  foldVar 0 $ Var "x"
+  ,foldVar 1 $ Dy (Var "x") A.Plus (lit 0)
+  
+  ,foldCon 100 (lit 2) (Dy (lit 1) A.Plus (lit 1))  
+  ,foldCon 101 (lit 65537) (Dy (lit 2) A.Plus (lit 65535))
+  ,foldCon 102 (lit (- two63)) (Dy (lit $ two63 - 1) A.Plus (lit 1))
  ]
+ where
+   two63 :: Integer
+   two63 = 9223372036854775808
+ 
+   foldVar :: Int -> ExprHelper -> Test
+   foldVar n e = testPass ("constantFoldTest " ++ show n) (buildExprPattern e) (constantFoldPass $ buildExpr e) state
+
+   foldCon :: Int -> ExprHelper -> ExprHelper -> Test
+   foldCon n exp orig = testPass ("constantFoldTest " ++ show n) (buildExprPattern exp) (constantFoldPass $ buildExpr orig) state
+
+   state :: State CompState ()
+   state = return ()
+
+   lit :: Integer -> ExprHelper
+   lit n = Lit $ int64Literal n
 
 tests :: Test
 tests = TestList