error test for Cradle.

test/CradleSpec.hs

@@ -51,6 +51,10 @@ spec = do
                   , cradlePackageConf = Just "test/data/cabal-dev/packages-7.6.2.conf"
                   }
 
+        it "throws an error if the sandbox does not exist" $ do
+            withDirectory_ "/" $
+                findCradle (Just "/") "7.4.1" `shouldThrow` anyIOException
+
 relativeCradle :: FilePath -> Cradle -> Cradle
 relativeCradle dir cradle = Cradle {
     cradleCurrentDir  = toRelativeDir dir  $  cradleCurrentDir  cradle