test: freeze the callstack for better failure messages

test/Spec.hs

@@ -11,6 +11,7 @@ import Types
 import Data.String (IsString (..))
 import Data.Text (Text)
 import Text.Parsec.Pos
+import GHC.Stack
 
 main :: IO ()
 main = hspec $ do
@@ -185,6 +186,7 @@ instance IsString (Doc String) where
 
 shouldLexTo :: String -> [(Int, Int, Token)] -> Expectation
 shouldLexTo input expected =
+   withFrozenCallStack $
     case lexer input of
         Right tokens -> do
             let actual = map (\(pos, tok) -> (sourceLine pos, sourceColumn pos, tok)) tokens