Add OrderedMap prototype

tests/Language/GraphQL/Execute/OrderedMapSpec.hs

@@ -0,0 +1,17 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE OverloadedStrings #-}
+module Language.GraphQL.Execute.OrderedMapSpec
+    ( spec
+    ) where
+
+import Language.GraphQL.Execute.OrderedMap (OrderedMap)
+import Test.Hspec (Spec, describe, it, shouldSatisfy)
+
+spec :: Spec
+spec =
+    describe "OrderedMap" $
+        it "creates an empty map" $
+            (mempty :: OrderedMap Int) `shouldSatisfy` null