test(pandoc): fix an occasionally erroneously failing test

src/Utils/Print.hs

@@ -119,8 +119,8 @@ appMeta f (P.Pandoc m bs) = P.Pandoc (f m) bs
 applyMetas :: (P.HasMeta p, Foldable t, P.ToMetaValue a) => t (Text, Maybe a) -> p -> p
 applyMetas metas doc = Fold.foldr act doc metas
   where
-    act (_, Nothing) acc = acc
-    act (k, Just v ) acc = P.setMeta k v acc
+    act (k, Just v) acc | notNull k = P.setMeta k v acc
+    act _           acc             =               acc
 
 
 -- | Add meta to pandoc. Existing variables will be overwritten.

test/PandocSpec.hs

@@ -24,13 +24,15 @@ newtype ArbitraryMeta = ArbitraryMeta { unArbitraryMeta :: Meta }
 newtype ArbitraryPandoc = ArbitraryPandoc { unArbitraryPandoc :: Pandoc }
   deriving newtype (Eq, Ord, Show, Read, Typeable)
 
+newtype ArbitraryMapText a = ArbitraryMapText { unArbitraryMapText :: [(Text, a)] }
+
 instance Arbitrary ArbitraryMeta where
   arbitrary = do
     (x1 :: Inlines) <- arbitrary
     (x2 :: [Inlines]) <- filter (not . Fold.null) <$> arbitrary
     (x3 :: Inlines) <- arbitrary
-    (x4 :: [(Text, Text)]) <- filter (not . T.null . fst) <$> arbitrary
-    (x5 :: [(Text, Bool)]) <- filter (not . T.null . fst) <$> arbitrary               
+    (x4 :: [(Text, Text)]) <- unArbitraryMapText <$> arbitrary
+    (x5 :: [(Text, Bool)]) <- unArbitraryMapText <$> arbitrary
     return $ ArbitraryMeta
           $ setMeta "title" x1
           $ setMeta "author" x2
@@ -44,6 +46,15 @@ instance Arbitrary ArbitraryPandoc where
     meta  <- arbitrary
     ArbitraryPandoc . Pandoc (unArbitraryMeta meta) <$> arbitrary
 
+nonEmptyString :: Gen Text
+nonEmptyString = T.pack <$> listOf1 arbitrary
+
+instance Arbitrary a => Arbitrary (ArbitraryMapText a) where
+  arbitrary =
+    let genKV = (,) <$> nonEmptyString <*> arbitrary
+    in ArbitraryMapText <$> listOf1 genKV
+
+
 
 -- For Lens Check _Meta required:
 --instance CoArbitrary Inline
@@ -59,13 +70,15 @@ spec = do
 
   describe "applyMetas" $ do
     it "should actually set values" $ do
-      (metaList, apd) <- generate arbitrary
+      (metaList0, apd) <- generate arbitrary
       let
+        metaList1 :: [(Text, Maybe MetaValue)] = second (Just . MetaString) <$> unArbitraryMapText metaList0
         pd = unArbitraryPandoc apd
-        (Pandoc metaNew _) = applyMetas (second (Just . MetaString) <$> metaList) pd
-        mlKeys = Set.fromList $ fst <$> metaList
-        metaList' = [(k,t) | (k, MetaString t) <- mlist metaNew, Set.member k mlKeys]
-      metaList' `shouldMatchList` metaList
+        (Pandoc metaNew _) = applyMetas metaList1 pd
+        metaMap1 = Map.fromList metaList1 -- remove duplicate keys
+        keys1 = Map.keysSet metaMap1
+        metaList' = [(k, Just t) | (k, t) <- mlist metaNew, k `Set.member` keys1]
+      metaList' `shouldMatchList` Map.toAscList metaMap1
 
     it "should preserve untouched settings" $ do
       (metaList, apd) <- generate arbitrary