testsuite: Fix racing prints in T21465wip/T23155

As noted in #23155, we previously failed to add flushes necessary to
ensure predictable output.

Fixes #23155.

3 files changed, 5 insertions, 2 deletions

diff --git a/testsuite/tests/rts/T21465/T21465.hs b/testsuite/tests/rts/T21465/T21465.hs
index 1465359054..4346f06d9d 100644
--- a/testsuite/tests/rts/T21465/T21465.hs
+++ b/testsuite/tests/rts/T21465/T21465.hs
@@ -1,10 +1,12 @@
 {-# LANGUAGE ForeignFunctionInterface #-}
 module Main where
 
+import System.IO
+
 foreign import ccall "test_c" testC :: IO ()
 
 helper :: IO ()
-helper = putStrLn "This is the helper function"
+helper = putStrLn "This is the helper function" >> hFlush stdout
 
 foreign export ccall helper :: IO ()
 
diff --git a/testsuite/tests/rts/T21465/T21465.stdout b/testsuite/tests/rts/T21465/T21465.stdout
index 2ae74934f3..bb8fe2203d 100644
--- a/testsuite/tests/rts/T21465/T21465.stdout
+++ b/testsuite/tests/rts/T21465/T21465.stdout
@@ -1,5 +1,4 @@
 This is the helper function
-Done.
  0: 01 01
  1: 02 02
  2: 03 03
@@ -16,3 +15,4 @@ Done.
 13: 0e 0e
 14: 0f 0f
 15: 10 10
+Done.
diff --git a/testsuite/tests/rts/T21465/T21465_c.c b/testsuite/tests/rts/T21465/T21465_c.c
index 3351027a91..dc93e6becf 100644
--- a/testsuite/tests/rts/T21465/T21465_c.c
+++ b/testsuite/tests/rts/T21465/T21465_c.c
@@ -25,4 +25,5 @@ void test_c() {
     for (int i = 0; i < 16; i++) {
         printf("%2i: %02x %02x\n", i, blah[i], foo[i]);
     }
+    fflush(stdout);
 }