diff --git a/lib/phpunit/classes/advanced_testcase.php b/lib/phpunit/classes/advanced_testcase.php
index 41a7da01b1e..7420ce40ab6 100644
--- a/lib/phpunit/classes/advanced_testcase.php
+++ b/lib/phpunit/classes/advanced_testcase.php
@@ -702,7 +702,7 @@ abstract class advanced_testcase extends base_testcase {
             }
 
             cron_prepare_core_renderer();
-            $this->setUser($user);
+            cron_setup_user($user);
 
             $task->execute();
             \core\task\manager::adhoc_task_complete($task);
diff --git a/lib/phpunit/tests/advanced_test.php b/lib/phpunit/tests/advanced_test.php
index 525325d2a38..769072a5516 100644
--- a/lib/phpunit/tests/advanced_test.php
+++ b/lib/phpunit/tests/advanced_test.php
@@ -33,8 +33,13 @@ defined('MOODLE_INTERNAL') || die();
  * @category   phpunit
  * @copyright  2012 Petr Skoda {@link http://skodak.org}
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ * @coversDefaultClass \advanced_testcase
  */
 class core_phpunit_advanced_testcase extends advanced_testcase {
+    public static function setUpBeforeClass(): void {
+        global $CFG;
+        require_once(__DIR__ . '/fixtures/adhoc_test_task.php');
+    }
 
     public function test_debugging() {
         global $CFG;
@@ -680,4 +685,53 @@ class core_phpunit_advanced_testcase extends advanced_testcase {
         self::resetAllData(false);
         self::assertFalse(core_useragent::get_user_agent_string(), 'It should not be set again, data was reset.');
     }
+
+    /**
+     * @covers ::runAdhocTasks
+     */
+    public function test_runadhoctasks_no_tasks_queued(): void {
+        $this->runAdhocTasks();
+        $this->expectOutputRegex('/^$/');
+    }
+
+    /**
+     * @covers ::runAdhocTasks
+     */
+    public function test_runadhoctasks_tasks_queued(): void {
+        $this->resetAfterTest(true);
+        $admin = get_admin();
+        \core\task\manager::queue_adhoc_task(new \core_phpunit\adhoc_test_task());
+        $this->runAdhocTasks();
+        $this->expectOutputRegex("/Task was run as {$admin->id}/");
+    }
+
+    /**
+     * @covers ::runAdhocTasks
+     */
+    public function test_runadhoctasks_with_existing_user_change(): void {
+        $this->resetAfterTest(true);
+        $admin = get_admin();
+
+        $this->setGuestUser();
+        \core\task\manager::queue_adhoc_task(new \core_phpunit\adhoc_test_task());
+        $this->runAdhocTasks();
+        $this->expectOutputRegex("/Task was run as {$admin->id}/");
+    }
+
+    /**
+     * @covers ::runAdhocTasks
+     */
+    public function test_runadhoctasks_with_existing_user_change_and_specified(): void {
+        global $USER;
+
+        $this->resetAfterTest(true);
+        $user = $this->getDataGenerator()->create_user();
+
+        $this->setGuestUser();
+        $task = new \core_phpunit\adhoc_test_task();
+        $task->set_userid($user->id);
+        \core\task\manager::queue_adhoc_task($task);
+        $this->runAdhocTasks();
+        $this->expectOutputRegex("/Task was run as {$user->id}/");
+    }
 }
diff --git a/lib/phpunit/tests/fixtures/adhoc_test_task.php b/lib/phpunit/tests/fixtures/adhoc_test_task.php
new file mode 100644
index 00000000000..090650fdc0c
--- /dev/null
+++ b/lib/phpunit/tests/fixtures/adhoc_test_task.php
@@ -0,0 +1,35 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle 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 General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+namespace core_phpunit;
+
+/**
+ * Fixtures for task tests.
+ *
+ * @package    core
+ * @category   phpunit
+ * @copyright  2023 Andrew Lyons <andrew@nicols.co.uk>
+ * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+class adhoc_test_task extends \core\task\adhoc_task {
+    /**
+     * Execute.
+     */
+    public function execute() {
+        global $USER;
+        mtrace("Task was run as {$USER->id}");
+    }
+}