1 files changed, 10 insertions, 4 deletions
diff --git a/libraries/base/tests/listThreads.hs b/libraries/base/tests/listThreads.hs
index 398afd0cc7..5037ea2e32 100644
--- a/libraries/base/tests/listThreads.hs
+++ b/libraries/base/tests/listThreads.hs
@@ -1,3 +1,6 @@
+import Data.Maybe
+import Control.Monad
+import qualified Data.Set as S
 import Control.Concurrent
 import Data.List (sort)
 import GHC.Conc.Sync
@@ -13,11 +16,14 @@ main = do
   mvar <- newEmptyMVar
   let mkThread n = do
         tid <- forkIO $ readMVar mvar
-        labelThread tid ("thread-"++show n)
+        let lbl = "thread-"++show n
+        labelThread tid lbl
+        return lbl
 
-  mapM_ mkThread [0..100]
+  expectedLabels <- S.fromList <$> mapM mkThread [0..100]
   threads <- listThreads
-  print $ length threads
-  print . sort =<< mapM threadLabel threads
+  labels <- S.fromList . catMaybes <$> mapM threadLabel threads
+  unless (S.null $ expectedLabels `S.difference` labels) $
+      putStrLn $ unlines [ "thread labels don't match", show expectedLabels, show labels ]
   putMVar mvar ()