test/helper: warn atomically

We want to avoid race conditions if tests become multithreaded
from Kernel#warn internally issuing a second write.

1 files changed, 1 insertions, 1 deletions

diff --git a/test/helper.rb b/test/helper.rb
index 7b8c1aa..c86f3e3 100644
--- a/test/helper.rb
+++ b/test/helper.rb
@@ -140,7 +140,7 @@ class DieIfUsed
   end
 
   def close
-    warn "INFO #$$ closed DieIfUsed #{@@n += 1}"
+    warn "INFO #$$ closed DieIfUsed #{@@n += 1}\n"
   end
 end