2 files changed, 26 insertions, 0 deletions
diff --git a/test/Spec.hs b/test/Spec.hs
index 7af988a3d7e3..27e26862e255 100644
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -6,6 +6,7 @@ import qualified Xanthous.GameSpec
 import qualified Xanthous.Generators.UtilSpec
 import qualified Xanthous.MessageSpec
 import qualified Xanthous.OrphansSpec
+import qualified Xanthous.UtilSpec
 import qualified Xanthous.Util.GraphicsSpec
 import qualified Xanthous.Util.InflectionSpec
 
@@ -21,6 +22,7 @@ test = testGroup "Xanthous"
   , Xanthous.MessageSpec.test
   , Xanthous.OrphansSpec.test
   , Xanthous.DataSpec.test
+  , Xanthous.UtilSpec.test
   , Xanthous.Util.GraphicsSpec.test
   , Xanthous.Util.InflectionSpec.test
   ]
diff --git a/test/Xanthous/UtilSpec.hs b/test/Xanthous/UtilSpec.hs
new file mode 100644
index 000000000000..1cfca1ffca76
--- /dev/null
+++ b/test/Xanthous/UtilSpec.hs
@@ -0,0 +1,24 @@
+module Xanthous.UtilSpec (main, test) where
+
+import Test.Prelude
+import Xanthous.Util
+
+main :: IO ()
+main = defaultMain test
+
+test :: TestTree
+test = testGroup "Xanthous.Util"
+  [ testGroup "smallestNotIn"
+    [ testCase "examples" $ do
+        smallestNotIn [7 :: Word, 3, 7] @?= 0
+        smallestNotIn [7 :: Word, 0, 1, 3, 7] @?= 2
+    , testProperty "returns an element not in the list" $ \(xs :: [Word]) ->
+        smallestNotIn xs `notElem` xs
+    , testProperty "pred return is in the list" $ \(xs :: [Word]) ->
+        let res = smallestNotIn xs
+        in res /= 0 ==> pred res `elem` xs
+    , testProperty "ignores order" $ \(xs :: [Word]) ->
+        forAll (shuffle xs) $ \shuffledXs ->
+          smallestNotIn xs === smallestNotIn shuffledXs
+    ]
+  ]