Test 1 (regression test copied from  MDL-60125 ): Open the main calendar Add a calendar event Confirm the month reloaded to show the correct month with the new event Drag/drop a calendar event Confirm the month reloaded to show the correct month with the new event Drag/drop a calendar event to a different month Confirm the month reloaded to show the correct month with the new event Use the navigation to move forward a month Confirm the month changed Reload the page Confirm that the same month is still shown Move forward a few more months Confirm the month changed each time Move back a few months Confirm the month changed each time Click the " Calendar " link in the breadcrumbs Change back and forth month a few times Confirm the month changed each time Open your dashboard and add the calendar block Use the navigation to move forward some months Confirm the month changed each time Use the navigation to move back some months Confirm the month changed each time Open a course and add the calendar block Use the navigation to move forward some months Confirm the month changed each time Use the navigation to move back some months Confirm the month changed each time Test 2: Install the Hijri calendar type ( https://github.com/rezaies/moodle-calendartype_hijri ) git clone https: //github.com/rezaies/moodle-calendartype_hijri calendar/type/hijri Log in as admin From the user menu, go to the preferences page, and then go to "Calendar preferences" Set your preferred calendar to Hijri Go to the calendar page Verify that there is no error on the page