diff --git a/src/Test/Simple.hs b/src/Test/Simple.hs
--- a/src/Test/Simple.hs
+++ b/src/Test/Simple.hs
@@ -47,7 +47,7 @@
             plan,
 
             -- * Test functions
-            ok, isnt, is, like, unlike,
+            ok, isnt, is, like, unlike, isRight,
 
             -- * Diagnostics
             loc, diag) where
@@ -146,6 +146,11 @@
 -- | Is @a@ unlike @b@?
 unlike :: (Show a, Show b, Likeable a b, Monad m) => a -> b -> TestSimpleT m Bool
 unlike a b = ok (not $ isLike a b) >>? diagVals "" (quote a) "matches" (quote b)
+
+-- | Is 'Either' right?
+isRight :: (Monad m, Show a) => Either a b -> TestSimpleT m Bool
+isRight (Right _) = ok True
+isRight (Left a) = ok False >>? diagVals "got Left:" (quote a) "expected:" "Right"
 
 -- | Outputs diagnostics message.
 diag :: Monad m => String -> TestSimpleT m ()
diff --git a/test-simple.cabal b/test-simple.cabal
--- a/test-simple.cabal
+++ b/test-simple.cabal
@@ -1,5 +1,5 @@
 Name:                test-simple
-Version:             0.1
+Version:             0.1.1
 License:             BSD3
 License-File:        COPYING
 Copyright:           Boris Sukholitko, 2012
diff --git a/tests/Main.hs b/tests/Main.hs
--- a/tests/Main.hs
+++ b/tests/Main.hs
@@ -78,16 +78,23 @@
     like err "#      got: '1'\n"
     like err "# expected: anything else\n"
 
+testEither :: ExitCode -> String -> String -> TestSimpleT IO Bool
+testEither ec out err = do
+    isnt ec ExitSuccess
+    like out "1..2"
+    like out "ok 1"
+    like err "got Left: '\"badleft\"'"
+
 testAll :: IO ()
 testAll = testSimpleMain $ do
-    plan 40
+    plan 44
     pn <- liftIO getExecutablePath
     mapM_ (runMyself pn) [ ("bbbf", testUnknown), ("ok1", testOk1), ("nok1", testNOk1)
                 , ("mism", testMismatch), ("isf", testIsFailure)
                 , ("likef", testLikeFailure), ("qloc", testLocationPrint)
                 , ("unlike", testOk1), ("fail_unlike", testUnlikeFailure)
                 , ("guard", testOk1), ("mplus", testMPlus), ("fail_mplus", testMPlusFail)
-                , ("guardisnt", testGuard) ]
+                , ("guardisnt", testGuard), ("either", testEither) ]
     where runMyself pn (arg, act) = do
                 (ec, out, err) <- liftIO $ readProcessWithExitCode pn [ arg ] ""
                 act ec out err
@@ -109,5 +116,9 @@
         [ "mplus" ] -> testSimpleMain $ (plan 1 >> ok True) >> (plan 1 >> ok True)
         [ "fail_mplus" ] -> testSimpleMain $ (plan 1 >> ok False) >> (plan 1 >> ok True)
         [ "guardisnt" ] -> testSimpleMain $ plan 1 >> (isnt (1::Int) 1 >>= guard) >> diag "DIAG"
+        [ "either" ] -> testSimpleMain $ do
+                            plan 2
+                            isRight (Right "hhh" :: Either Int String)
+                            isRight (Left "badleft" :: Either String Int)
         _ -> error $ "Unknown: " ++ show as