Give a diff on test failure

1 files changed, 2 insertions, 1 deletions

diff --git a/tests/runtests.hs b/tests/runtests.hs
index 321938b3..d3fa71de 100644
--- a/tests/runtests.hs
+++ b/tests/runtests.hs
@@ -39,7 +39,8 @@ check modules = do
         ref <- readFile reffile
         if not $ haddockEq out ref
           then do
-            putStrLn $ "Output for " ++ mod ++ " has changed! Exiting."
+            putStrLn $ "Output for " ++ mod ++ " has changed! Exiting with diff:"
+            system $ "diff " ++ reffile ++ " " ++ outfile
             exitFailure
           else do
             putStrLn $ "Pass: " ++ mod