Write tests for Cabal's JSON lib

Cabal-tests/Cabal-tests.cabal

@@ -40,6 +40,7 @@ test-suite unit-tests
     UnitTests.Distribution.Types.GenericPackageDescription
     UnitTests.Distribution.Utils.CharSet
     UnitTests.Distribution.Utils.Generic
+    UnitTests.Distribution.Utils.Json
     UnitTests.Distribution.Utils.NubList
     UnitTests.Distribution.Utils.ShortText
     UnitTests.Distribution.Utils.Structured

Cabal-tests/tests/UnitTests.hs

@@ -23,6 +23,7 @@ import qualified UnitTests.Distribution.Simple.Utils
 import qualified UnitTests.Distribution.System
 import qualified UnitTests.Distribution.Utils.CharSet
 import qualified UnitTests.Distribution.Utils.Generic
+import qualified UnitTests.Distribution.Utils.Json
 import qualified UnitTests.Distribution.Utils.NubList
 import qualified UnitTests.Distribution.Utils.ShortText
 import qualified UnitTests.Distribution.Utils.Structured
@@ -57,6 +58,8 @@ tests mtimeChangeCalibrated =
         UnitTests.Distribution.Simple.Utils.tests ghcPath
     , testGroup "Distribution.Utils.Generic"
         UnitTests.Distribution.Utils.Generic.tests
+    , testGroup "Distribution.Utils.Json" $
+        UnitTests.Distribution.Utils.Json.tests
     , testGroup "Distribution.Utils.NubList"
         UnitTests.Distribution.Utils.NubList.tests
     , testGroup "Distribution.Utils.ShortText"

Cabal-tests/tests/UnitTests/Distribution/Utils/Json.hs

+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE OverloadedStrings #-}
+module UnitTests.Distribution.Utils.Json
+    ( tests
+    ) where
+
+import Distribution.Utils.Json
+
+import Test.Tasty
+import Test.Tasty.HUnit
+
+tests :: [TestTree]
+tests =
+    [ testCase "escapes strings correctly" $
+      renderJson (JsonString "foo\"bar") @?= "\"foo\\\"bar\""
+    , testCase "renders empty list" $
+      renderJson (JsonArray []) @?= "[]"
+    , testCase "renders singleton list" $
+      renderJson (JsonArray [JsonString "foo\"bar"]) @?= "[\"foo\\\"bar\"]"
+    , testCase "renders list" $
+      renderJson (JsonArray [JsonString "foo\"bar", JsonString "baz"]) @?= "[\"foo\\\"bar\",\"baz\"]"
+    , testCase "renders empty object" $
+      renderJson (JsonObject []) @?= "{}"
+    , testCase "renders singleton object" $
+      renderJson (JsonObject [("key", JsonString "foo\"bar")]) @?= "{\"key\":\"foo\\\"bar\"}"
+    , testCase "renders object" $
+      renderJson (JsonObject
+                    [ ("key", JsonString "foo\"bar")
+                    , ("key2", JsonString "baz")])
+          @?= "{\"key\":\"foo\\\"bar\",\"key2\":\"baz\"}"
+    , testCase "renders number" $
+      renderJson (JsonNumber 0) @?= "0"
+    , testCase "renders negative number" $
+      renderJson (JsonNumber (-1)) @?= "-1"
+    , testCase "renders big number" $
+      renderJson (JsonNumber 5000000) @?= "5000000"
+    , testCase "renders bool" $ do
+      renderJson (JsonBool True) @?= "true"
+      renderJson (JsonBool False) @?= "false"
+    , testCase "renders null" $ do
+      renderJson JsonNull @?= "null"
+    ]