1 files changed, 18 insertions, 0 deletions

diff --git a/tests/test_wcsncat_n_one.c b/tests/test_wcsncat_n_one.c
new file mode 100644
index 0000000..23de28e
--- /dev/null
+++ b/tests/test_wcsncat_n_one.c
@@ -0,0 +1,18 @@
+#include "common.h"
+
+#include <wchar.h>
+
+int main(int argc, char** argv) {
+  wchar_t buffer[8] = {0};
+  wcsncat(buffer, L"1234567", 7);
+  printf("%ls\n", buffer);
+
+  /* n=1, buffer has 7 wchars.
+   * 7+1+1 = 9 > 8 → overflow. Even n=1 can overflow a nearly-full buffer. */
+  CHK_FAIL_START
+  wcsncat(buffer, L"X", 1);
+  CHK_FAIL_END
+
+  printf("%ls\n", buffer);
+  return ret;
+}