diff --git a/hspec-dirstream.cabal b/hspec-dirstream.cabal
--- a/hspec-dirstream.cabal
+++ b/hspec-dirstream.cabal
@@ -1,5 +1,5 @@
 name:                hspec-dirstream
-version:             0.2.0.0
+version:             0.3.0.0
 synopsis:            Helper functions to simplify adding integration tests.
 description:         This package uses [hspec](http://hackage.haskell.org/package/hspec) and [dirstream](http://hackage.haskell.org/package/dirstream) to provide easy-to-use functions for integration tests.
 homepage:            https://hub.darcs.net/vmchale/hspec-dirstream
diff --git a/src/Test/Hspec/Dirstream.hs b/src/Test/Hspec/Dirstream.hs
--- a/src/Test/Hspec/Dirstream.hs
+++ b/src/Test/Hspec/Dirstream.hs
@@ -8,6 +8,8 @@
     ( -- Functions to generate a `Spec`
       testFiles
     , testFilesIO
+    , testFilesErr
+    , testFilesPredicate
     -- * Helper functions for dealing with file extensions
     , F.extension
     , Test.Hspec.Dirstream.hasExtension
@@ -61,14 +63,42 @@
           -> SpecWith ()
 testFiles dir p f = runSafeT $ runEffect $ paths dir p >-> mapS (testFile f)
 
+-- | A version of the above where the return value can be any 'IO'.
 testFilesIO :: FilePath -> (F.FilePath -> Bool) -> (String -> IO String) -> SpecWith ()
 testFilesIO dir p f = runSafeT $ runEffect $ paths dir p >-> mapS (testFileIO f)
 
+-- | This function checks that each file returns a value satisfying the
+-- predicate.
+testFilesPredicate :: (Show a, Eq a)
+                   => FilePath -- ^ Directory containing test data
+                   -> (F.FilePath -> Bool) -- ^ Filter on file extensions
+                   -> (String -> a) -- ^ Function to process the string
+                   -> (a -> Bool) -- ^ Predicate to check the result
+                   -> SpecWith ()
+testFilesPredicate dir p f pr = runSafeT $ runEffect $ paths dir p >-> mapS (testFilePredicate f pr)
+
 testFileIO :: (String -> IO String) -> String -> SpecWith ()
 testFileIO fun f = it f $ do
     sample <- readFile f
     expected <- readFile (replaceExtension f ".out")
     fun sample >>= (`shouldBe` expected)
+
+-- | This function simply tests that each file returns a 'Left' value and that
+-- the error message contained therein matches the contents of the appropriate
+-- file.
+testFilesErr :: (Show b, Eq b) => FilePath -> (F.FilePath -> Bool) -> (String -> Either String b) -> SpecWith ()
+testFilesErr dir p f = runSafeT $ runEffect $ paths dir p >-> mapS (testFileErr f)
+
+testFilePredicate :: (Eq a, Show a) => (String -> a) -> (a -> Bool) -> String -> SpecWith ()
+testFilePredicate fun p f = it f $ do
+    sample <- readFile f
+    fun sample `shouldSatisfy` p
+
+testFileErr :: (Eq b, Show b) => (String -> Either String b) -> String -> SpecWith ()
+testFileErr fun f = it f $ do
+    sample <- readFile f
+    expected <- readFile (replaceExtension f ".out")
+    fun sample `shouldBe` Left expected
 
 testFile :: (Eq a, Show a) => (String -> Either a String) -> String -> SpecWith ()
 testFile fun f = it f $ do
diff --git a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -13,3 +13,5 @@
             testFiles "test/data" (hasExtension "hs") ((pure :: a -> Either String a) . tail)
     describe "testFilesIO" $
             testFilesIO "test/data" (hasExtension "hs") (pure . tail)
+    describe "testFilesPredicate" $
+            testFilesPredicate "test/data" (hasExtension "hs") tail ((>= 0) . length)