Add type-inference tests (#1023)

Closes #1021.

dhall/dhall.cabal

@@ -368,6 +368,8 @@ Extra-Source-Files:
     dhall-lang/tests/typecheck/success/prelude/Text/concatSep/*.dhall
     dhall-lang/tests/typecheck/success/simple/access/*.dhall
     dhall-lang/tests/typecheck/success/simple/*.dhall
+    dhall-lang/tests/type-inference/success/simple/*.dhall
+    dhall-lang/tests/type-inference/success/unit/*.dhall
     tests/format/*.dhall
     tests/lint/success/*.dhall
     tests/diff/*.dhall
@@ -533,6 +535,7 @@ Test-Suite tasty
         Dhall.Test.Regression
         Dhall.Test.Tutorial
         Dhall.Test.TypeCheck
+        Dhall.Test.TypeInference
         Dhall.Test.Util
     Build-Depends:
         base                      >= 4        && < 5   ,

dhall/tests/Dhall/Test/Main.hs

@@ -14,6 +14,7 @@ import qualified Dhall.Test.QuickCheck
 import qualified Dhall.Test.Regression
 import qualified Dhall.Test.Tutorial
 import qualified Dhall.Test.TypeCheck
+import qualified Dhall.Test.TypeInference
 import qualified GHC.IO.Encoding
 import qualified System.Directory
 import qualified System.Environment
@@ -30,6 +31,8 @@ getAllTests = do
 
     typecheckingTests <- Dhall.Test.TypeCheck.getTests
 
+    typeinferenceTests <- Dhall.Test.TypeInference.getTests
+
     importingTests <- Dhall.Test.Import.getTests
 
     lintTests <- Dhall.Test.Lint.getTests
@@ -42,6 +45,7 @@ getAllTests = do
                 , parsingTests
                 , importingTests
                 , typecheckingTests
+                , typeinferenceTests
                 , formattingTests
                 , lintTests
                 , diffTests

dhall/tests/Dhall/Test/TypeInference.hs

@@ -0,0 +1,49 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Dhall.Test.TypeInference where
+
+import Data.Monoid (mempty, (<>))
+import Data.Text (Text)
+import Prelude hiding (FilePath)
+import Test.Tasty (TestTree)
+
+import qualified Data.Text         as Text
+import qualified Data.Text.IO      as Text.IO
+import qualified Dhall.Core        as Core
+import qualified Dhall.Import      as Import
+import qualified Dhall.Parser      as Parser
+import qualified Dhall.Test.Util   as Test.Util
+import qualified Dhall.TypeCheck   as TypeCheck
+import qualified Test.Tasty        as Tasty
+import qualified Test.Tasty.HUnit  as Tasty.HUnit
+import qualified Turtle
+
+getTests :: IO TestTree
+getTests = do
+    successTests <- Test.Util.discover (Turtle.chars <* "A.dhall") successTest (Turtle.lstree "./dhall-lang/tests/type-inference/success")
+
+    let testTree = Tasty.testGroup "type-inference tests"
+            [ successTests
+            ]
+
+    return testTree
+
+successTest :: Text -> TestTree
+successTest prefix = do
+    Tasty.HUnit.testCase (Text.unpack prefix) $ do
+        value <- expr "A.dhall"
+
+        expectedType <- expr "B.dhall"
+
+        inferredType <- Core.throws (TypeCheck.typeOf value)
+
+        let message = "The inferred type did not match the expected type"
+
+        Tasty.HUnit.assertEqual message expectedType inferredType
+  where
+    expr suffix = do
+        code <- Text.IO.readFile (Text.unpack prefix <> suffix)
+
+        e <- Core.throws (Parser.exprFromText mempty code)
+
+        Import.assertNoImports (Core.denote e)