Add testsuite for the library interface

brittany.cabal

@@ -359,3 +359,40 @@ test-suite littests
   if flag(brittany-dev) {
     ghc-options: -O0 -Werror -fobject-code
   }
+
+test-suite libinterfacetests
+  if flag(brittany-dev-lib) {
+    buildable: False
+  } else {
+    buildable: True
+  }
+  type:             exitcode-stdio-1.0
+  default-language: Haskell2010
+  build-depends:
+    { brittany
+    , base
+    , text
+    , transformers
+    , hspec >=2.4.1 && <2.5
+    }
+  ghc-options:      -Wall
+  main-is:          Main.hs
+  other-modules:    
+  hs-source-dirs:   src-libinterfacetests
+  default-extensions: {
+    FlexibleContexts
+    FlexibleInstances
+    ScopedTypeVariables
+    MonadComprehensions
+    LambdaCase
+    MultiWayIf
+    KindSignatures
+  }
+  ghc-options: {
+    -Wall
+    -j
+    -fno-warn-unused-imports
+    -fno-warn-orphans
+    -rtsopts
+    -with-rtsopts "-M2G"
+  }

src-libinterfacetests/Main.hs

@@ -0,0 +1,32 @@
+module Main where
+
+
+
+import           Test.Hspec
+import           Language.Haskell.Brittany
+import qualified Data.Text as Text
+import qualified System.Exit as Exit
+import           Control.Monad.IO.Class
+
+
+
+main :: IO ()
+main = hspec $ do
+  describe "library interface basic functionality" $ do
+    it "gives properly formatted result for valid input" $ do
+      let
+        input = Text.pack $ unlines
+          ["func = [00000000000000000000000, 00000000000000000000000, 00000000000000000000000, 00000000000000000000000]"]
+      let expected = Text.pack $ unlines
+            [ "func ="
+            , "  [ 00000000000000000000000"
+            , "  , 00000000000000000000000"
+            , "  , 00000000000000000000000"
+            , "  , 00000000000000000000000"
+            , "  ]"
+            ]
+      output <- liftIO $ pureModuleTransform mempty input
+      input `shouldSatisfy` \_ -> case output of
+        Right x | x == expected -> True
+        _                       -> False
+