Implement proper Cabal tests out of the existing structure

SJW.cabal

@@ -60,3 +60,16 @@ benchmark big-src
                      , time
   default-language:    Haskell2010
   ghc-options:         -Wall
+
+test-suite tests
+  type:                detailed-0.9
+  test-module:         Tests
+  build-depends:       base >=4.11 && <4.13
+                     , Cabal
+                     , directory
+                     , filepath
+                     , random
+                     , SJW
+  hs-source-dirs:      test
+  default-language:    Haskell2010
+  ghc-options:         -Wall

test/Tests.hs

@@ -0,0 +1,42 @@
+module Tests (
+    tests
+  ) where
+
+import Distribution.TestSuite
+import SJW (compile, source)
+import System.FilePath ((</>))
+import Text.Printf (printf)
+
+testData :: FilePath
+testData = "test" </> "data"
+
+checkResult :: (String, Bool) -> IO Progress
+checkResult (dirName, expected) = do
+  result <- either failed passed =<< compile (source [testData </> dirName])
+  return . Finished $ if result == expected then Pass else Fail (explain message)
+  where
+    failed s = putStrLn s>> return False
+    passed _ = return True
+    explain = uncurry (printf "Compilation %sed when it was expected to %s")
+    message = if expected then ("fail", "succeed") else ("succeed", "fail")
+
+makeTest :: (String, Bool) -> TestInstance
+makeTest (patternName, expected) = testInstance
+  where
+    testInstance = TestInstance {
+          run = checkResult (patternName, expected)
+        , name = patternName
+        , tags = []
+        , options = []
+        , setOption = \_ _ -> Right testInstance
+      }
+
+tests :: IO [Test]
+tests = return $ (Test . makeTest) <$> [
+      ("cycle", False)
+    , ("diamond", True)
+    , ("loop", False)
+    , ("q", False)
+    , ("simple", True)
+    , ("triangle", True)
+  ]