test: add test case for issue #34637

(cherry picked from commit 88d186e4829bc7ef4a4253fe2bf4857903bca830)

diff --git a/test/units/TEST-17-UDEV.diskseq.sh b/test/units/TEST-17-UDEV.diskseq.sh
new file mode 100755 (executable)
index 0000000..0cb717f
--- /dev/null
+++ b/test/units/TEST-17-UDEV.diskseq.sh
@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: LGPL-2.1-or-later
+# shellcheck disable=SC2010
+# shellcheck disable=SC2317
+set -ex
+set -o pipefail
+
+# shellcheck source=test/units/util.sh
+. "$(dirname "$0")"/util.sh
+
+# This is a test case for issue #34637.
+
+at_exit() (
+    set +e
+
+    systemctl stop test-diskseq.service || :
+    rm -f /run/systemd/system/test-diskseq.service
+    systemctl daemon-reload
+
+    [[ -d "$TMPDIR" ]] && rm -rf "$TMPDIR"
+
+    udevadm control --log-level=info
+)
+
+trap at_exit EXIT
+
+udevadm control --log-level=debug
+
+TMPDIR="$(mktemp -d)"
+truncate -s 16M "$TMPDIR"/foo.raw
+mkfs.ext4 -L foo "$TMPDIR"/foo.raw
+
+mkdir -p /run/systemd/system/
+cat >/run/systemd/system/test-diskseq.service <<EOF
+[Unit]
+StartLimitIntervalSec=0
+[Service]
+ExecStart=false
+Restart=on-failure
+MountImages=$TMPDIR/foo.raw:/var
+EOF
+systemctl daemon-reload
+
+udevadm settle
+
+# If an initrd from the host is used, stack directories for by-diskseq symlinks
+# may already exist. Save the number of the directories here.
+NUM_DISKSEQ_EXPECTED=$(ls /run/udev/links | grep -c by-diskseq || :)
+
+systemctl start --no-block test-diskseq.service
+
+for _ in {0..100}; do
+    sleep .1
+    assert_eq "$(ls /run/udev/links | grep -c by-diskseq || :)" "$NUM_DISKSEQ_EXPECTED"
+done
+
+exit 0