CTest by design combines stdout and stderr. It would be nice if they were separate.

CMakeLists.txt

cmake_minimum_required(VERSION 3.19)

project(piper LANGUAGES C)

enable_testing()

add_executable(piper main.c)

add_test(NAME piper COMMAND piper)

main.c

#include <stdio.h>
int main(void) {
fprintf(stdout, "stdout pipe\n");
fprintf(stderr, "stderr pipe\n");
return 0;
}

run.sh

cmake -B build && cmake --build build

# stdout and stderr combined
ctest --test-dir build -V 2>/dev/null

# no output
ctest --test-dir build -V 1>/dev/null