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diff --git a/testsuite/tests/patsyn/should_fail/T11667.hs b/testsuite/tests/patsyn/should_fail/T11667.hs
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+++ b/testsuite/tests/patsyn/should_fail/T11667.hs
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+{-# LANGUAGE PatternSynonyms, GADTs #-}
+module T11667 where
+
+{-
+The following four pattern synonym declarations should give valid
+error messages
+-}
+
+-- Check if we mention no explicit type signature (or the correct
+-- signature "Eq a => Maybe a")
+pattern Pat1 :: Eq a => Maybe a
+pattern Pat1 <- Just 42
+
+-- Check if we mention no explicit type signature (or the correct
+-- signature "forall b. () => forall a. b ~ Bool => a -> b -> (b, T)")
+data T where MkT :: a -> T
+pattern Pat2 :: () => b ~ Bool => a -> b -> (b, T)
+pattern Pat2 x y = (y, MkT x)
+
+-- Check if we do not tell the user that we could not deduce (Show a)
+-- from the "required" context. Also, check if we do not give the
+-- possible fix that suggests to add (Show a) to the "required" context.
+pattern Pat3 :: Eq a => Show a => a -> Maybe a
+pattern Pat3 x <- Just x
+
+-- Check if we return a valid error message concerning the missing
+-- constraint (Num a) when the bidirectional pattern synonym is used
+-- in an expression context
+data S a where MkS :: (Num a, Show a) => a -> S a
+pattern Pat4 :: (Eq a) => (Show a) => S a
+pattern Pat4 = MkS 42