diff --git a/src/Config.hs b/src/Config.hs
index 28ad2c6..9a55b7d 100644
--- a/src/Config.hs
+++ b/src/Config.hs
@@ -8,6 +8,7 @@ module Config (
 #ifdef TEST
 , ConfigFile(..)
 , readConfigFilesFrom
+, tryReadFile
 #endif
 ) where
 
diff --git a/test/GHC/DiagnosticSpec.hs b/test/GHC/DiagnosticSpec.hs
index f5c7977..abd88ec 100644
--- a/test/GHC/DiagnosticSpec.hs
+++ b/test/GHC/DiagnosticSpec.hs
@@ -13,16 +13,22 @@ import           GHC.Diagnostic
 test :: HasCallStack => FilePath -> Spec
 test name = it name $ do
   err <- translate <$> ghc ["-fno-diagnostics-show-caret"]
-  Just diagnostic <- parse . encodeUtf8 <$> ghc ["-fdiagnostics-as-json"]
+  json <- encodeUtf8 <$> ghc ["-fdiagnostics-as-json"]
+  ensureFile (dir </> "err.out") (encodeUtf8 err)
+  ensureFile (dir </> "err.json") json
+  Just diagnostic <- return $ parse json
   decodeUtf8 (format diagnostic) `shouldBe` err
   where
+    dir :: FilePath
+    dir = "test" </> "assets" </> name
+
     ghc :: [String] -> IO String
     ghc args = do
       requireGhc [9,10]
       bin <- lookupGhc <$> getEnvironment
       let
         process :: CreateProcess
-        process = proc bin (args ++ ["test/assets" </> name </> "Foo.hs"])
+        process = proc bin (args ++ [dir </> "Foo.hs"])
       (_, _, err) <- readCreateProcessWithExitCode process ""
       return err
 
diff --git a/test/Helper.hs b/test/Helper.hs
index 9a92bbb..61ff0a0 100644
--- a/test/Helper.hs
+++ b/test/Helper.hs
@@ -24,6 +24,7 @@ module Helper (
 , to_json
 
 , requireGhc
+, ensureFile
 ) where
 
 import           Prelude hiding (span)
@@ -39,10 +40,12 @@ import           Test.Mockery.Directory as Imports (touch)
 import           System.Environment
 import qualified System.Timeout
 
+import qualified Data.ByteString as ByteString
 import           Data.ByteString.Lazy (toStrict)
 import           Data.Aeson (ToJSON, encode)
 
 import           Run ()
+import           Config (tryReadFile)
 import           Util
 import           Language.Haskell.GhciWrapper
 
@@ -127,3 +130,9 @@ requireGhc (makeVersion -> required) = do
   env <- getEnvironment
   let Just ghcVersion = lookupGhcVersion env >>= parseVersion
   when (ghcVersion < required) pending
+
+ensureFile :: FilePath -> ByteString -> IO ()
+ensureFile name new = do
+  old <- tryReadFile name
+  unless (old == Just new) $ do
+    ByteString.writeFile name new
diff --git a/test/assets/non-existing/err.json b/test/assets/non-existing/err.json
new file mode 100644
index 0000000..910ffed
--- /dev/null
+++ b/test/assets/non-existing/err.json
@@ -0,0 +1 @@
+{"version":"1.0","ghcVersion":"ghc-9.10.1","span":null,"severity":"Error","code":49196,"message":["Can't find test/assets/non-existing/Foo.hs"],"hints":[]}
diff --git a/test/assets/non-existing/err.out b/test/assets/non-existing/err.out
new file mode 100644
index 0000000..61e02cb
--- /dev/null
+++ b/test/assets/non-existing/err.out
@@ -0,0 +1,3 @@
+<no location info>: error: [GHC-49196]
+    Can't find test/assets/non-existing/Foo.hs
+
diff --git a/test/assets/use-BlockArguments/err.json b/test/assets/use-BlockArguments/err.json
new file mode 100644
index 0000000..611d0cb
--- /dev/null
+++ b/test/assets/use-BlockArguments/err.json
@@ -0,0 +1 @@
+{"version":"1.0","ghcVersion":"ghc-9.10.1","span":{"file":"test/assets/use-BlockArguments/Foo.hs","start":{"line":5,"column":10},"end":{"line":5,"column":22}},"severity":"Error","code":52095,"message":["Unexpected do block in function application:\n    do return ()"],"hints":["Use parentheses.","Perhaps you intended to use BlockArguments"]}
diff --git a/test/assets/use-BlockArguments/err.out b/test/assets/use-BlockArguments/err.out
new file mode 100644
index 0000000..8670c8f
--- /dev/null
+++ b/test/assets/use-BlockArguments/err.out
@@ -0,0 +1,7 @@
+test/assets/use-BlockArguments/Foo.hs:5:10: error: [GHC-52095]
+    Unexpected do block in function application:
+        do return ()
+    Suggested fixes:
+      • Use parentheses.
+      • Perhaps you intended to use BlockArguments
+
diff --git a/test/assets/variable-not-in-scope-perhaps-use/err.json b/test/assets/variable-not-in-scope-perhaps-use/err.json
new file mode 100644
index 0000000..e3c301f
--- /dev/null
+++ b/test/assets/variable-not-in-scope-perhaps-use/err.json
@@ -0,0 +1 @@
+{"version":"1.0","ghcVersion":"ghc-9.10.1","span":{"file":"test/assets/variable-not-in-scope-perhaps-use/Foo.hs","start":{"line":2,"column":7},"end":{"line":2,"column":14}},"severity":"Error","code":88464,"message":["Variable not in scope: filter_"],"hints":["Perhaps use `filter' (imported from Prelude)"]}
diff --git a/test/assets/variable-not-in-scope-perhaps-use/err.out b/test/assets/variable-not-in-scope-perhaps-use/err.out
new file mode 100644
index 0000000..dba1a4f
--- /dev/null
+++ b/test/assets/variable-not-in-scope-perhaps-use/err.out
@@ -0,0 +1,4 @@
+test/assets/variable-not-in-scope-perhaps-use/Foo.hs:2:7: error: [GHC-88464]
+    Variable not in scope: filter_
+    Suggested fix: Perhaps use `filter' (imported from Prelude)
+
diff --git a/test/assets/variable-not-in-scope/Spec.hs b/test/assets/variable-not-in-scope/Spec.hs
deleted file mode 100644
index 5f2becf..0000000
--- a/test/assets/variable-not-in-scope/Spec.hs
+++ /dev/null
@@ -1,2 +0,0 @@
-module Foo where
-foo = bar
diff --git a/test/assets/variable-not-in-scope/err.json b/test/assets/variable-not-in-scope/err.json
new file mode 100644
index 0000000..7377670
--- /dev/null
+++ b/test/assets/variable-not-in-scope/err.json
@@ -0,0 +1 @@
+{"version":"1.0","ghcVersion":"ghc-9.10.1","span":{"file":"test/assets/variable-not-in-scope/Foo.hs","start":{"line":2,"column":7},"end":{"line":2,"column":10}},"severity":"Error","code":88464,"message":["Variable not in scope: bar"],"hints":[]}
diff --git a/test/assets/variable-not-in-scope/err.out b/test/assets/variable-not-in-scope/err.out
new file mode 100644
index 0000000..1f30f36
--- /dev/null
+++ b/test/assets/variable-not-in-scope/err.out
@@ -0,0 +1,3 @@
+test/assets/variable-not-in-scope/Foo.hs:2:7: error: [GHC-88464]
+    Variable not in scope: bar
+