testsuite: Add tests for #16943

libraries/base/tests/T16943a.hs

+module Main(main) where
+
+scoreWeek = scanr (:) [] $ repeat True
+
+main = seq scoreWeek (putStrLn "good")
+

libraries/base/tests/T16943a.stdout

+good
+

libraries/base/tests/T16943b.hs

+module Main(main) where
+
+scoreWeek :: [Int] -> [[Int]]
+scoreWeek xs =
+  take 168
+  $ scanr (:) []
+  -- $ take (3*168)
+  $ cycle xs
+
+main = print $ length $ scoreWeek [1,2..168]
+

libraries/base/tests/T16943b.stdout

+168
+

libraries/base/tests/all.T

@@ -251,3 +251,5 @@ test('T13896', normal, compile_and_run, [''])
 test('T13167', fragile_for(16536, ['threaded2']), compile_and_run, [''])
 test('T15349', [exit_code(1), expect_broken_for(15349, ['ghci'])], compile_and_run, [''])
 test('T16111', exit_code(1), compile_and_run, [''])
+test('T16943a', normal, compile_and_run, [''])
+test('T16943b', normal, compile_and_run, [''])