tests: misc: test that /proc/self/comm is properly set

This tests the fix introduced by commit ee9b9aff8 (all: set
/proc/self/comm to the program name in the single binary, 2026-10-17).

* tests/misc/proc-self-comm.sh: New file.
* tests/local.mk (all_tests): Add the new test.

tests/local.mk

@@ -188,6 +188,7 @@ all_tests =					\
   tests/misc/responsive.sh			\
   tests/misc/no-fork.sh				\
   tests/misc/exec-bad-unicode.sh		\
+  tests/misc/proc-self-comm.sh			\
   tests/misc/traversal-missing.sh		\
   tests/misc/tty-quoting.sh			\
   tests/misc/uname-labeled.sh			\

tests/misc/proc-self-comm.sh

@@ -0,0 +1,52 @@
+#!/bin/sh
+# Test that the program name in /proc/self/comm is properly set.
+
+# Copyright (C) 2026 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ cat
+
+test -f /proc/self/comm || skip_ '/proc/self/comm is required'
+
+# Set up variables to execute 'cat' from its absolute path and,
+# if available, through the single binary.
+abs_cat=$(cmd_exe cat) || framework_failure_
+single_binary=$(cmd_exe coreutils) &&
+  single_binary_cat="$single_binary --coreutils-prog=cat"
+
+if test -n "$single_binary_cat" && ! $single_binary_cat /dev/null 2>err; then
+  grep "^coreutils: unknown program 'cat'$" err || framework_failure_
+  single_binary=
+  single_binary_cat=
+fi
+
+# If we are not using --enable-single-binary=symlinks, then set
+# up a symlink in the test directory to ensure this gets tested.
+if test -n "$single_binary" && ! test -L "$abs_cat"; then
+  mkdir dir || framework_failure_
+  ln -s "$single_binary" dir/cat || framework_failure_
+  symlink_cat='env PATH='"$(pwd)/dir:$PATH"' cat'
+fi
+
+echo 'cat' >exp || framework_failure_
+for prog in cat "$abs_cat" "$single_binary_cat" "$symlink_cat"; do
+  test -z "$prog" && continue
+  $prog /proc/self/comm >out 2>err || fail=1
+  compare exp out || fail=1
+  compare /dev/null err || fail=1
+done
+
+Exit $fail