tests: Add initial alternatives test

This makes sure that the system is setup properly and that the migration
script will do the right thing on older systems.

See: coreos/fedora-coreos-tracker#1818
See: coreos/fedora-coreos-tracker#677
See: https://docs.fedoraproject.org/en-US/fedora-coreos/alternatives/

tests/kola/files/alternatives

@@ -0,0 +1,46 @@
+#!/bin/bash
+## kola:
+##   description: Verify that the alternatives config is properly migrated and test the migration
+
+# See
+# - https://github.com/coreos/fedora-coreos-tracker/issues/1818
+
+set -xeuo pipefail
+
+# shellcheck disable=SC1091
+. "$KOLA_EXT_DATA/commonlib.sh"
+
+if test -e "/var/lib/alternatives"; then
+    ls -al "/var/lib/alternatives"
+    fatal "Error: Found '/var/lib/alternatives' which should not exists"
+fi
+if ! test -d "/etc/alternatives"; then
+    fatal "Error: '/etc/alternatives' is missing"
+fi
+if ! test -d "/etc/alternatives-admindir"; then
+    fatal "Error: '/etc/alternatives-admindir' is missing"
+fi
+
+# To test the migration we will re-create the setup from an older FCOS node
+
+# First, reset iptables to the legacy backend
+alternatives --set iptables /usr/sbin/iptables-legacy
+if [[ $(alternatives --display iptables | grep -c "link currently points to /usr/sbin/iptables-legacy") != "1" ]]; then
+    fatal "Could not set iptables to legacy backend for testing"
+fi
+if [[ $(iptables --version | grep -c "legacy") != "1" ]]; then
+    fatal "Could not set iptables to legacy backend for testing"
+fi
+
+# Then re-create the broken alternatives folder in /var
+install -dm0755 /var/lib/alternatives
+
+# Do the migration, explicitely using the new configuration directory to ignore
+# the empty one in /var
+alternatives --admindir /etc/alternatives-admindir --set iptables /usr/sbin/iptables-nft
+if [[ $(alternatives --admindir /etc/alternatives-admindir --display iptables | grep -c "link currently points to /usr/sbin/iptables-nft") != "1" ]]; then
+    fatal "Could not set iptables to nft backend for migration"
+fi
+if [[ $(iptables --version | grep -c "nf_tables") != "1" ]]; then
+    fatal "Error: iptables not reset to nftables backend"
+fi