tests: add a simple test that bootctl output is valid json

python's json.tool module is used because it does validation. jq is more forgiving.
Also, json is in the stdlib, so it should be always available.

meson.build

@@ -2583,7 +2583,7 @@ if conf.get('HAVE_BLKID') == 1 and conf.get('HAVE_GNU_EFI') == 1
                 boot_link_with = [libsystemd_static, libshared_static]
         endif
 
-        public_programs += executable(
+        exe = executable(
                 'bootctl',
                 'src/boot/bootctl.c',
                 include_directories : includes,
@@ -2592,6 +2592,14 @@ if conf.get('HAVE_BLKID') == 1 and conf.get('HAVE_GNU_EFI') == 1
                                 versiondep],
                 install_rpath : rootpkglibdir,
                 install : true)
+        public_programs += exe
+
+        if want_tests != 'false'
+                test('test-bootctl-json',
+                     test_bootctl_json_sh,
+                     args : exe.full_path(),
+                     depends : exe)
+        endif
 
         public_programs += executable(
                 'systemd-bless-boot',

test/meson.build

@@ -89,6 +89,7 @@ if install_tests
                      install_dir : testdata_dir)
 endif
 
+test_bootctl_json_sh = find_program('test-bootctl-json.sh')
 test_fstab_generator_sh = find_program('test-fstab-generator.sh')
 test_network_generator_conversion_sh = find_program('test-network-generator-conversion.sh')
 test_systemctl_enable_sh = find_program('test-systemctl-enable.sh')

test/test-bootctl-json.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: LGPL-2.1-or-later
+set -e
+set -o pipefail
+
+bootctl="${1:?}"
+
+"$bootctl" --no-pager list >/dev/null || {
+    echo "$bootctl list failed, skipping tests" 1>&2
+    exit 77
+}
+
+set -x
+
+"$bootctl" list --json=pretty | python3 -m json.tool >/dev/null
+"$bootctl" list --json=short | python3 -m json.tool >/dev/null
+
+command -v jq >/dev/null || {
+    echo "jq is not available, skipping jq tests" 1>&2
+    exit 0
+}
+
+"$bootctl" list --json=pretty | jq . >/dev/null
+"$bootctl" list --json=short | jq . >/dev/null