implement expect (accidentally looked at docs for nanospec instead of hspec)

Author: chessai

test/ArrayFire/ArithSpec.hs

@@ -7,6 +7,7 @@ import Test.Hspec
 import Foreign.C
 
 import qualified ArrayFire as A
+import qualified System.Exit as E
 
 spec :: Spec
 spec =
@@ -101,3 +102,10 @@ actual `shouldBeEps` expected = expect err_msg (cmpEps actual expected)
       let x :: Double
           x = fromIntegral $ Prelude.abs $ actual - expected
       in x <= 1e-14
+
+expect :: String -> Bool -> Expectation
+expect label f = if f
+  then pure ()
+  else do
+    putStrLn label
+    E.exitFailure