Add property test for added lookupDefault

nix/haskell-dependencies.nix

@@ -19,6 +19,7 @@ haskellPackages:
       megaparsec
       optparse-applicative
       parser-combinators
+      quickcheck-instances
       retry
       text
       unix

package.yaml

@@ -55,3 +55,4 @@ tests:
     - hspec-expectations
     - directory
     - QuickCheck
+    - quickcheck-instances

test/KeyMapSpec.hs

@@ -0,0 +1,25 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module KeyMapSpec where
+
+import Data.Text (Text)
+import Test.Hspec
+import Test.QuickCheck
+import Test.QuickCheck.Instances ()
+
+import qualified Data.HashMap.Internal.Strict as HM
+
+import qualified KeyMap as KM
+
+mapFirst :: (a->b) -> [(a,c)] -> [(b,c)]
+mapFirst _ [] = []
+mapFirst f ((x,y) : rest) = (f x, y) : mapFirst f rest
+
+spec :: SpecWith ()
+spec =
+  describe "KeyMap" $ do
+    it "lookupDefault matches the HashMap implementation" $
+      property $ \((fallback :: Text), key, mapping) ->
+        let keyMapValue = KM.lookupDefault fallback (KM.fromText key) (KM.fromList $ mapFirst KM.fromText mapping)
+            hashMapValue = HM.lookupDefault fallback key (HM.fromList mapping)
+        in keyMapValue `shouldBe` hashMapValue