use $() instead of backtiks for command substitution, as it gives a more consistent behavior.

See https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap02.html#tag_23_02_06_03 for more details

Author: baldurmen

manifests/backup/xtrabackup.pp

@@ -63,7 +63,7 @@
 
   $daily_cron_data = ($incremental_backups) ? {
     true  => {
-      'directories' => "--incremental-basedir=${backupdir} --target-dir=${backupdir}/`date +%F_%H-%M-%S`",
+      'directories' => "--incremental-basedir=${backupdir} --target-dir=${backupdir}/$(date +%F_%H-%M-%S)",
       'weekday'     => '1-6',
     },
     false => {

spec/classes/mysql_backup_xtrabackup_spec.rb

@@ -44,7 +44,7 @@ class { 'mysql::server': }
           is_expected.to contain_cron('xtrabackup-daily')
             .with(
               ensure: 'present',
-              command: '/usr/local/sbin/xtrabackup.sh --incremental-basedir=/tmp --target-dir=/tmp/`date +%F_%H-%M-%S` --backup',
+              command: '/usr/local/sbin/xtrabackup.sh --incremental-basedir=/tmp --target-dir=/tmp/$(date +%F_%H-%M-%S) --backup',
               user: 'root',
               hour: '23',
               minute: '5',
@@ -101,7 +101,7 @@ class { 'mysql::server': }
           is_expected.to contain_cron('xtrabackup-daily')
             .with(
               ensure: 'present',
-              command: '/usr/local/sbin/xtrabackup.sh --incremental-basedir=/tmp --target-dir=/tmp/`date +%F_%H-%M-%S` --backup --skip-ssl',
+              command: '/usr/local/sbin/xtrabackup.sh --incremental-basedir=/tmp --target-dir=/tmp/$(date +%F_%H-%M-%S) --backup --skip-ssl',
               user: 'root',
               hour: '23',
               minute: '5',