MDL-54751 phpunit: Support adhoc module and section deletion in phpunit

Created a new phpunit util function run_all_adhoc_tasks which runs any
pending tasks, for use in unit tests. Added new recyclebin and course
unit tests covering the new functionality.

lib/phpunit/classes/util.php

@@ -819,4 +819,21 @@ class phpunit_util extends testing_util {
             return 'en_AU.UTF-8';
         }
     }
+
+    /**
+     * Executes all adhoc tasks in the queue. Useful for testing asynchronous behaviour.
+     *
+     * @return void
+     */
+    public static function run_all_adhoc_tasks() {
+        $now = time();
+        while (($task = \core\task\manager::get_next_adhoc_task($now)) !== null) {
+            try {
+                $task->execute();
+                \core\task\manager::adhoc_task_complete($task);
+            } catch (Exception $e) {
+                \core\task\manager::adhoc_task_failed($task);
+            }
+        }
+    }
 }