add more tests

Author: hdgarrood

tests/Data/Map.purs

@@ -2,6 +2,7 @@ module Tests.Data.Map where
 
 import Debug.Trace
 
+import Control.Alt ((<|>))
 import Data.Maybe
 import Data.Tuple
 import Data.Array (map, length, nubBy)
@@ -166,6 +167,9 @@ mapTests = do
   trace "Union is idempotent"
   quickCheck $ \m1 m2 -> (m1 `M.union` m2) == ((m1 `M.union` m2) `M.union` (m2 :: M.Map SmallKey Number))
 
+  trace "Union prefers left"
+  quickCheck $ \m1 m2 k -> M.lookup k (M.union m1 (m2 :: M.Map SmallKey Number)) == (M.lookup k m1 <|> M.lookup k m2)
+
   trace "unionWith"
   for_ [Tuple (+) 0, Tuple (*) 1] $ \(Tuple op ident) ->
     quickCheck $ \m1 m2 k ->
@@ -174,6 +178,19 @@ mapTests = do
            Nothing -> not (M.member k m1 || M.member k m2)
            Just v -> v == op (fromMaybe ident (M.lookup k m1)) (fromMaybe ident (M.lookup k m2))
 
+  trace "unionWith argument order"
+  quickCheck $ \m1 m2 k ->
+    let u   = M.unionWith (-) m1 m2 :: M.Map SmallKey Number
+        in1 = M.member k m1
+        v1  = M.lookup k m1
+        in2 = M.member k m2
+        v2  = M.lookup k m2
+    in case M.lookup k u of
+          Just v | in1 && in2 -> Just v == ((-) <$> v1 <*> v2)
+          Just v | in1        -> Just v == v1
+          Just v              -> Just v == v2
+          Nothing             -> not (in1 || in2)
+
   trace "size"
   quickCheck $ \xs ->
     let xs' = nubBy ((==) `on` fst) xs