Revert "Simplify test suite"

This reverts commit 8f2625dc87.

source/test-suite/Main.hs

@@ -1,12 +1,14 @@
+import qualified Control.Exception as Exception
 import qualified Control.Monad as Monad
 import qualified Data.List as List
 import qualified Language.Haskell.Brittany.Main as Brittany
 import qualified System.Directory as Directory
 import qualified System.FilePath as FilePath
+import qualified System.IO as IO
 import qualified Test.Hspec as Hspec
 
 main :: IO ()
-main = Hspec.hspec . Hspec.parallel $ do
+main = Hspec.hspec $ do
   let directory = "data"
   entries <- Hspec.runIO $ Directory.listDirectory directory
   Monad.forM_ (List.sort entries) $ \entry ->
@@ -15,7 +17,8 @@ main = Hspec.hspec . Hspec.parallel $ do
       Just slug -> Hspec.it slug $ do
         let input = FilePath.combine directory entry
         expected <- readFile input
-        let output = FilePath.combine "output" entry
+        actual <- withTemporaryFile $ \output handle -> do
+          IO.hClose handle
           Directory.copyFile input output
           Brittany.mainWith
             "brittany"
@@ -26,9 +29,19 @@ main = Hspec.hspec . Hspec.parallel $ do
             , "inplace"
             , output
             ]
-        actual <- readFile output
+          readFile output
         Literal actual `Hspec.shouldBe` Literal expected
 
+withTemporaryFile :: (FilePath -> IO.Handle -> IO a) -> IO a
+withTemporaryFile callback = do
+  directory <- Directory.getTemporaryDirectory
+  let
+    acquire = IO.openTempFile directory "brittany-.hs"
+    release filePath handle = do
+      IO.hClose handle
+      Directory.removeFile filePath
+  Exception.bracket acquire (uncurry release) (uncurry callback)
+
 newtype Literal
   = Literal String
   deriving Eq