test: introduce TEST-83-BTRFS

The Ubuntu CIs are deny-listed because the shipped
btrfs-progs is too old, i.e. doesn't support the
recently-added 'filesystem mkswapfile' command.

test/units/testsuite-83.service

@@ -0,0 +1,8 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[Unit]
+Description=TEST-83-BTRFS
+
+[Service]
+ExecStartPre=rm -f /failed /testok
+ExecStart=/usr/lib/systemd/tests/testdata/units/%N.sh
+Type=oneshot

test/units/testsuite-83.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: LGPL-2.1-or-later
+set -eux
+set -o pipefail
+
+TEST_BTRFS_OFFSET=/usr/lib/systemd/tests/unit-tests/manual/test-btrfs-physical-offset
+
+SWAPFILE=/var/tmp/swapfile
+
+btrfs filesystem mkswapfile -s 10m "$SWAPFILE"
+sync -f "$SWAPFILE"
+
+offset_btrfs_progs="$(btrfs inspect-internal map-swapfile -r "$SWAPFILE")"
+echo "btrfs-progs: $offset_btrfs_progs"
+
+offset_btrfs_util="$("$TEST_BTRFS_OFFSET" "$SWAPFILE")"
+echo "btrfs-util: $offset_btrfs_util"
+
+(( offset_btrfs_progs == offset_btrfs_util ))
+
+rm -f "$SWAPFILE"
+
+/usr/lib/systemd/tests/unit-tests/manual/test-btrfs
+
+touch /testok