test result value, return URL in Right branch, document meaning in haddocks

yesod-test/Yesod/Test.hs

@@ -695,12 +695,15 @@ get url = request $ do
     setUrl url
 
 -- | Follow a redirect, if the last response was a redirect.
+-- | Return Left with an error message if not a redirect
+-- | Return Right with the redirected URL if it was.
+--
 -- ==== __Examples__
 -- > get HomeR
 --
 -- > followRedirect
 followRedirect :: Yesod site
-               =>  YesodExample site (Either T.Text ())
+               =>  YesodExample site (Either T.Text T.Text)
 followRedirect = do
   mr <- getResponse
   case mr of
@@ -711,7 +714,8 @@ followRedirect = do
        else do
          case lookup "Location" (simpleHeaders r) of
           Nothing -> return $ Left "followRedirect called, but no location header set"
-          Just h -> get (TE.decodeUtf8 h) >> return (Right ())
+          Just h -> let url = TE.decodeUtf8 h in
+                     get url  >> return (Right url)
 
 -- | Sets the HTTP method used by the request.
 --

yesod-test/test/main.hs

@@ -20,7 +20,7 @@ import Data.Monoid ((<>))
 import Control.Applicative
 import Network.Wai (pathInfo, requestHeaders)
 import Data.Maybe (fromMaybe)
-import Data.Either (isLeft)
+import Data.Either (isLeft, isRight)
 import Control.Exception.Lifted(try, SomeException)
 
 import Data.ByteString.Lazy.Char8 ()
@@ -219,14 +219,16 @@ main = hspec $ do
         yit "follows 303 redirects when requested" $ do
             get ("/redirect303" :: Text)
             statusIs 303
-            followRedirect
+            r <- followRedirect
+            liftIO $ assertBool "expected a Right from a 303 redirect" $ isRight r
             statusIs 200
             bodyContains "we have been successfully redirected"
 
         yit "follows 301 redirects when requested" $ do
             get ("/redirect301" :: Text)
             statusIs 301
-            followRedirect
+            r <- followRedirect
+            liftIO $ assertBool "expected a Right from a 301 redirect" $ isRight r
             statusIs 200
             bodyContains "we have been successfully redirected"
 
@@ -235,7 +237,7 @@ main = hspec $ do
             get ("/" :: Text)
             statusIs 200
             r <- followRedirect
-            liftIO $ assertBool "expected exception" $ isLeft r
+            liftIO $ assertBool "expected a Left when not a redirect" $ isLeft r
 
 instance RenderMessage LiteApp FormMessage where
     renderMessage _ _ = defaultFormMessage