From e2f84e6ba9f1a6135d3bb33fd0b881a5d90cf606 Mon Sep 17 00:00:00 2001
From: Viktor Szakats <commit@vsz.me>
Date: Mon, 27 Apr 2026 10:49:45 +0200
Subject: [PATCH] tunits: initialize global `tool_stderr`

To avoid difficult to track down crashes when a tested function ends up
outputing a message via `errorf()`, `warnf()` or siblings.

Cherry-picked from #21449

Closes #21454
---
 tests/libtest/first.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/tests/libtest/first.c b/tests/libtest/first.c
index 08d9a9363b..e4e9dbd8c8 100644
--- a/tests/libtest/first.c
+++ b/tests/libtest/first.c
@@ -27,6 +27,10 @@
 #include <locale.h> /* for setlocale() */
 #endif
 
+#if defined(UNITTESTS) && !defined(BUILDING_LIBCURL)
+#include "tool_stderr.h"  /* for tool_init_stderr() */
+#endif
+
 int select_wrapper(int nfds, fd_set *rd, fd_set *wr, fd_set *exc,
                    struct timeval *tv)
 {
@@ -276,6 +280,10 @@ int main(int argc, const char **argv)
       testnum = (int)num;
   }
 
+#if defined(UNITTESTS) && !defined(BUILDING_LIBCURL)
+  tool_init_stderr();
+#endif
+
   result = entry_func(URL);
   curl_mfprintf(stderr, "Test ended with result %d\n", result);