diff --git a/plugins/libcalendaring/tests/RecurrenceTest.php b/plugins/libcalendaring/tests/RecurrenceTest.php
index f2dc3c16..eeb922ad 100644
--- a/plugins/libcalendaring/tests/RecurrenceTest.php
+++ b/plugins/libcalendaring/tests/RecurrenceTest.php
@@ -1,473 +1,477 @@
 <?php
 
 /**
  * libcalendaring_recurrence tests
  *
  * @author Aleksander Machniak <machniak@apheleia-it.ch>
  *
  * Copyright (C) 2022, Apheleia IT AG <contact@apheleia-it.ch>
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
  * published by the Free Software Foundation, either version 3 of the
  * License, or (at your option) any later version.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  * GNU Affero General Public License for more details.
  *
  * You should have received a copy of the GNU Affero General Public License
  * along with this program. If not, see <http://www.gnu.org/licenses/>.
  */
 
 class RecurrenceTest extends PHPUnit\Framework\TestCase
 {
     private $plugin;
 
     public function setUp(): void
     {
         $rcube = rcmail::get_instance();
         $rcube->plugins->load_plugin('libcalendaring', true, true);
 
         $this->plugin = $rcube->plugins->get_plugin('libcalendaring');
     }
 
     /**
      * Data for test_end()
      */
     public function data_end()
     {
         return [
             // non-recurring
             [
                 [
                     'recurrence' => [],
                     'start' => new DateTime('2017-08-31 11:00:00'),
                 ],
                 '2017-08-31 11:00:00', // expected result
             ],
             // daily
             [
                 [
                     'recurrence' => ['FREQ' => 'DAILY', 'INTERVAL' => '1', 'COUNT' => 2],
                     'start' => new DateTime('2017-08-31 11:00:00'),
                 ],
                 '2017-09-01 11:00:00',
             ],
             // weekly
             [
                 [
                     'recurrence' => ['FREQ' => 'WEEKLY', 'COUNT' => 3],
                     'start' => new DateTime('2017-08-31 11:00:00'), // Thursday
                 ],
                 '2017-09-14 11:00:00',
             ],
             // UNTIL
             [
                 [
                     'recurrence' => ['FREQ' => 'WEEKLY', 'COUNT' => 3, 'UNTIL' => new DateTime('2017-09-07 11:00:00')],
                     'start' => new DateTime('2017-08-31 11:00:00'), // Thursday
                 ],
                 '2017-09-07 11:00:00',
             ],
             // Infinite recurrence, no count, no until
             [
                 [
                     'recurrence' => ['FREQ' => 'WEEKLY', 'INTERVAL' => '1'],
                     'start' => new DateTime('2017-08-31 11:00:00'), // Thursday
                 ],
                 '2084-09-21 11:00:00',
             ],
 
             // TODO: Test an event with EXDATE/RDATEs
         ];
     }
     /**
      * Data for test_first_occurrence()
      */
     public function data_first_occurrence()
     {
         // TODO: BYYEARDAY, BYWEEKNO, BYSETPOS, WKST
 
         return [
             // non-recurring
             [
                 [],                                     // recurrence data
                 '2017-08-31 11:00:00',                       // start date
                 '2017-08-31 11:00:00',                       // expected result
             ],
             // daily
             [
                 ['FREQ' => 'DAILY', 'INTERVAL' => '1'], // recurrence data
                 '2017-08-31 11:00:00',                       // start date
                 '2017-08-31 11:00:00',                       // expected result
             ],
             // TODO: this one is not supported by the Calendar UI
 /*
             array(
                 array('FREQ' => 'DAILY', 'INTERVAL' => '1', 'BYMONTH' => 1),
                 '2017-08-31 11:00:00',
                 '2018-01-01 11:00:00',
             ),
 */
             // weekly
             [
                 ['FREQ' => 'WEEKLY', 'INTERVAL' => '1'],
                 '2017-08-31 11:00:00', // Thursday
                 '2017-08-31 11:00:00',
             ],
             [
                 ['FREQ' => 'WEEKLY', 'INTERVAL' => '1', 'BYDAY' => 'WE'],
                 '2017-08-31 11:00:00', // Thursday
                 '2017-09-06 11:00:00',
             ],
             [
                 ['FREQ' => 'WEEKLY', 'INTERVAL' => '1', 'BYDAY' => 'TH'],
                 '2017-08-31 11:00:00', // Thursday
                 '2017-08-31 11:00:00',
             ],
             [
                 ['FREQ' => 'WEEKLY', 'INTERVAL' => '1', 'BYDAY' => 'FR'],
                 '2017-08-31 11:00:00', // Thursday
                 '2017-09-01 11:00:00',
             ],
             [
                 ['FREQ' => 'WEEKLY', 'INTERVAL' => '2'],
                 '2017-08-31 11:00:00', // Thursday
                 '2017-08-31 11:00:00',
             ],
             [
                 ['FREQ' => 'WEEKLY', 'INTERVAL' => '3', 'BYDAY' => 'WE'],
                 '2017-08-31 11:00:00', // Thursday
                 '2017-09-20 11:00:00',
             ],
             [
                 ['FREQ' => 'WEEKLY', 'INTERVAL' => '1', 'BYDAY' => 'WE', 'COUNT' => 1],
                 '2017-08-31 11:00:00', // Thursday
                 '2017-09-06 11:00:00',
             ],
             [
                 ['FREQ' => 'WEEKLY', 'INTERVAL' => '1', 'BYDAY' => 'WE', 'UNTIL' => '2017-09-01'],
                 '2017-08-31 11:00:00', // Thursday
                 '',
             ],
             // monthly
             [
                 ['FREQ' => 'MONTHLY', 'INTERVAL' => '1'],
                 '2017-09-08 11:00:00',
                 '2017-09-08 11:00:00',
             ],
             [
                 ['FREQ' => 'MONTHLY', 'INTERVAL' => '1', 'BYMONTHDAY' => '8,9'],
                 '2017-08-31 11:00:00',
                 '2017-09-08 11:00:00',
             ],
             [
                 ['FREQ' => 'MONTHLY', 'INTERVAL' => '1', 'BYMONTHDAY' => '8,9'],
                 '2017-09-08 11:00:00',
                 '2017-09-08 11:00:00',
             ],
             [
                 ['FREQ' => 'MONTHLY', 'INTERVAL' => '1', 'BYDAY' => '1WE'],
                 '2017-08-16 11:00:00',
                 '2017-09-06 11:00:00',
             ],
             [
                 ['FREQ' => 'MONTHLY', 'INTERVAL' => '1', 'BYDAY' => '-1WE'],
                 '2017-08-16 11:00:00',
                 '2017-08-30 11:00:00',
             ],
             [
                 ['FREQ' => 'MONTHLY', 'INTERVAL' => '2'],
                 '2017-09-08 11:00:00',
                 '2017-09-08 11:00:00',
             ],
             [
                 ['FREQ' => 'MONTHLY', 'INTERVAL' => '2', 'BYMONTHDAY' => '8'],
                 '2017-08-31 11:00:00',
                 '2017-09-08 11:00:00', // ??????
             ],
             // yearly
             [
                 ['FREQ' => 'YEARLY', 'INTERVAL' => '1'],
                 '2017-08-16 12:00:00',
                 '2017-08-16 12:00:00',
             ],
             [
                 ['FREQ' => 'YEARLY', 'INTERVAL' => '1', 'BYMONTH' => '8'],
                 '2017-08-16 12:00:00',
                 '2017-08-16 12:00:00',
             ],
 /*
             // Not supported by Sabre (requires BYMONTH too)
             array(
                 array('FREQ' => 'YEARLY', 'INTERVAL' => '1', 'BYDAY' => '-1MO'),
                 '2017-08-16 11:00:00',
                 '2017-12-25 11:00:00',
             ),
 */
             [
                 ['FREQ' => 'YEARLY', 'INTERVAL' => '1', 'BYMONTH' => '8', 'BYDAY' => '-1MO'],
                 '2017-08-16 11:00:00',
                 '2017-08-28 11:00:00',
             ],
             [
                 ['FREQ' => 'YEARLY', 'INTERVAL' => '1', 'BYMONTH' => '1', 'BYDAY' => '1MO'],
                 '2017-08-16 11:00:00',
                 '2018-01-01 11:00:00',
             ],
             [
                 ['FREQ' => 'YEARLY', 'INTERVAL' => '1', 'BYMONTH' => '1,9', 'BYDAY' => '1MO'],
                 '2017-08-16 11:00:00',
                 '2017-09-04 11:00:00',
             ],
             [
                 ['FREQ' => 'YEARLY', 'INTERVAL' => '2'],
                 '2017-08-16 11:00:00',
                 '2017-08-16 11:00:00',
             ],
             [
                 ['FREQ' => 'YEARLY', 'INTERVAL' => '2', 'BYMONTH' => '8'],
                 '2017-08-16 11:00:00',
                 '2017-08-16 11:00:00',
             ],
 /*
             // Not supported by Sabre (requires BYMONTH too)
             array(
                 array('FREQ' => 'YEARLY', 'INTERVAL' => '2', 'BYDAY' => '-1MO'),
                 '2017-08-16 11:00:00',
                 '2017-12-25 11:00:00',
             ),
 */
             // on dates (FIXME: do we really expect the first occurrence to be on the start date?)
             [
                 ['RDATE' => [new DateTime('2017-08-10 11:00:00 Europe/Warsaw')]],
                 '2017-08-01 11:00:00',
                 '2017-08-01 11:00:00',
             ],
         ];
     }
 
     /**
      * Test for libcalendaring_recurrence::end()
      *
      * @dataProvider data_end
      */
     public function test_end($event, $expected)
     {
         $recurrence = new libcalendaring_recurrence($this->plugin, $event);
 
         $end = $recurrence->end();
 
         $this->assertSame($expected, $end ? $end->format('Y-m-d H:i:s') : $end);
     }
 
     /**
      * Test for libcalendaring_recurrence::first_occurrence()
      *
      * @dataProvider data_first_occurrence
      */
     public function test_first_occurrence($recurrence_data, $start, $expected)
     {
         $start = new DateTime($start);
         if (!empty($recurrence_data['UNTIL'])) {
             $recurrence_data['UNTIL'] = new DateTime($recurrence_data['UNTIL']);
         }
 
         $recurrence = $this->plugin->get_recurrence();
 
+        StderrMock::start();
         $recurrence->init($recurrence_data, $start);
         $first = $recurrence->first_occurrence();
+        StderrMock::stop();
 
         $this->assertEquals($expected, $first ? $first->format('Y-m-d H:i:s') : '');
     }
 
     /**
      * Test for libcalendaring_recurrence::first_occurrence() for all-day events
      *
      * @dataProvider data_first_occurrence
      */
     public function test_first_occurrence_allday($recurrence_data, $start, $expected)
     {
         $start = new libcalendaring_datetime($start);
         $start->_dateonly = true;
 
         if (!empty($recurrence_data['UNTIL'])) {
             $recurrence_data['UNTIL'] = new DateTime($recurrence_data['UNTIL']);
         }
 
         $recurrence = $this->plugin->get_recurrence();
 
+        StderrMock::start();
         $recurrence->init($recurrence_data, $start);
         $first = $recurrence->first_occurrence();
+        StderrMock::stop();
 
         $this->assertEquals($expected, $first ? $first->format('Y-m-d H:i:s') : '');
 
         if ($expected) {
             $this->assertTrue($first->_dateonly);
         }
     }
 
     /**
      * Test for an event with invalid recurrence
      */
     public function test_invalid_recurrence_event()
     {
         date_default_timezone_set('Europe/Berlin');
 
         // This is an event with no RRULE, but one RDATE, however the RDATE is cancelled by EXDATE.
         // This normally causes Sabre\VObject\Recur\NoInstancesException. We make sure it does not happen.
         // The same will probably happen on any event without recurrence passed to libcalendring_vcalendar.
 
         $vcal = <<<EOF
             BEGIN:VCALENDAR
             VERSION:2.0
             PRODID:-//Apple Inc.//iCal 5.0.3//EN
             CALSCALE:GREGORIAN
             BEGIN:VEVENT
             UID:fb1cb690-b963-4ea5-b58f-ac9773e36d9a
             DTSTART;TZID=Europe/Berlin:20210604T093000
             DTEND;TZID=Europe/Berlin:20210606T093000
             RDATE:20210604T073000Z
             EXDATE;TZID=Europe/Berlin:20210604T093000
             DTSTAMP:20210528T091628Z
             LAST-MODIFIED:20210528T091628Z
             CREATED:20210528T091213Z
             END:VEVENT
             END:VCALENDAR
             EOF;
 
         $ical = new libcalendaring_vcalendar();
         $event = $ical->import($vcal)[0];
 
         $recurrence = new libcalendaring_recurrence($this->plugin, $event);
 
         $this->assertSame($event['start']->format('Y-m-d H:i:s'), $recurrence->end()->format('Y-m-d H:i:s'));
         $this->assertSame($event['start']->format('Y-m-d H:i:s'), $recurrence->first_occurrence()->format('Y-m-d H:i:s'));
         $this->assertFalse($recurrence->next_start());
         $this->assertFalse($recurrence->next_instance());
     }
 
     /**
      * Test for libcalendaring_recurrence::next_instance()
      */
     public function test_next_instance()
     {
         date_default_timezone_set('America/New_York');
 
         $start = new libcalendaring_datetime('2017-08-31 11:00:00', new DateTimeZone('Europe/Berlin'));
         $event = [
             'start'      => $start,
             'recurrence' => ['FREQ' => 'WEEKLY', 'INTERVAL' => '1'],
             'allday'     => true,
         ];
 
         $recurrence = new libcalendaring_recurrence($this->plugin, $event);
         $next       = $recurrence->next_instance();
 
         $this->assertEquals($start->format('2017-09-07 H:i:s'), $next['start']->format('Y-m-d H:i:s'), 'Same time');
         $this->assertEquals($start->getTimezone()->getName(), $next['start']->getTimezone()->getName(), 'Same timezone');
         $this->assertTrue($next['start']->_dateonly, '_dateonly flag');
     }
 
     /**
      * Test for libcalendaring_recurrence::next_instance()
      */
     public function test_next_instance_exdate()
     {
         date_default_timezone_set('America/New_York');
 
         $start = new libcalendaring_datetime('2023-01-18 10:00:00', new DateTimeZone('Europe/Berlin'));
         $end = new libcalendaring_datetime('2023-01-18 10:30:00', new DateTimeZone('Europe/Berlin'));
         $event = [
             'start' => $start,
             'end' => $end,
             'recurrence' => [
                 'FREQ' => 'DAILY',
                 'INTERVAL' => '1',
                 'EXDATE' => [
                     // Exclude the start date
                     new libcalendaring_datetime('2023-01-18 10:00:00', new DateTimeZone('Europe/Berlin')),
                 ],
             ],
         ];
 
         $recurrence = new libcalendaring_recurrence($this->plugin, $event);
 
         $next = $recurrence->next_instance();
 
         $this->assertEquals('2023-01-19 10:00:00', $next['start']->format('Y-m-d H:i:s'));
         $this->assertEquals('Europe/Berlin', $next['start']->getTimezone()->getName());
         $this->assertFalse($next['start']->_dateonly);
 
         $next = $recurrence->next_instance();
 
         $this->assertEquals('2023-01-20 10:00:00', $next['start']->format('Y-m-d H:i:s'));
         $this->assertEquals('Europe/Berlin', $next['start']->getTimezone()->getName());
         $this->assertFalse($next['start']->_dateonly);
     }
 
     /**
      * Test for libcalendaring_recurrence::next_instance()
      */
     public function test_next_instance_dst()
     {
         date_default_timezone_set('America/New_York');
 
         $start = new libcalendaring_datetime('2021-03-10 10:00:00', new DateTimeZone('Europe/Berlin'));
         $end = new libcalendaring_datetime('2021-03-10 10:30:00', new DateTimeZone('Europe/Berlin'));
         $event = [
             'start' => $start,
             'end' => $end,
             'recurrence' => [
                 'FREQ' => 'MONTHLY',
                 'INTERVAL' => '1',
             ],
         ];
 
         $recurrence = new libcalendaring_recurrence($this->plugin, $event);
 
         $next = $recurrence->next_instance();
 
         $this->assertEquals('2021-04-10 10:00:00', $next['start']->format('Y-m-d H:i:s'));
         $this->assertEquals('Europe/Berlin', $next['start']->getTimezone()->getName());
 
         $next = $recurrence->next_instance();
 
         $this->assertEquals('2021-05-10 10:00:00', $next['start']->format('Y-m-d H:i:s'));
         $this->assertEquals('Europe/Berlin', $next['start']->getTimezone()->getName());
 
         $start = new libcalendaring_datetime('2021-10-10 10:00:00', new DateTimeZone('Europe/Berlin'));
         $end = new libcalendaring_datetime('2021-10-10 10:30:00', new DateTimeZone('Europe/Berlin'));
         $event = [
             'start' => $start,
             'end' => $end,
             'recurrence' => [
                 'FREQ' => 'MONTHLY',
                 'INTERVAL' => '1',
             ],
         ];
 
         $recurrence = new libcalendaring_recurrence($this->plugin, $event);
 
         $next = $recurrence->next_instance();
 
         $this->assertEquals('2021-11-10 10:00:00', $next['start']->format('Y-m-d H:i:s'));
         $this->assertEquals('Europe/Berlin', $next['start']->getTimezone()->getName());
 
         $next = $recurrence->next_instance();
 
         $this->assertEquals('2021-12-10 10:00:00', $next['start']->format('Y-m-d H:i:s'));
         $this->assertEquals('Europe/Berlin', $next['start']->getTimezone()->getName());
 
         $next = $recurrence->next_instance();
         $next = $recurrence->next_instance();
         $next = $recurrence->next_instance();
         $next = $recurrence->next_instance();
 
         $this->assertEquals('2022-04-10 10:00:00', $next['start']->format('Y-m-d H:i:s'));
         $this->assertEquals('Europe/Berlin', $next['start']->getTimezone()->getName());
 
     }
 }