test for Cabal and CabalApi.

test/Expectation.hs

@@ -1,8 +1,15 @@
 module Expectation where
 
 import Test.Hspec
+import System.Directory
+import Control.Exception as E
 
 shouldContain :: Eq a => [a] -> a -> Expectation
 shouldContain containers element = do
     let res = element `elem` containers
     res `shouldBe` True
+
+withDirectory :: FilePath -> IO a -> IO a
+withDirectory dir action = bracket getCurrentDirectory
+                                   setCurrentDirectory
+                                   (\_ -> setCurrentDirectory dir >> action)