Only in b: dist-newstyle
diff -ur a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs	2001-09-09 03:46:40.000000000 +0200
+++ b/test/Spec.hs	2025-03-07 12:32:09.836426856 +0100
@@ -10,6 +10,7 @@
 module Main where
 
 import Data.Bifunctor
+import Control.Monad (when)
 import Control.Monad.Writer (WriterT (..))
 import Data.Coerce (coerce)
 import Data.Monoid (Any (..), Ap (..))