diff --git a/lib/phpunit/classes/database_driver_testcase.php b/lib/phpunit/classes/database_driver_testcase.php
index a255208276a..9c2ec342e96 100644
--- a/lib/phpunit/classes/database_driver_testcase.php
+++ b/lib/phpunit/classes/database_driver_testcase.php
@@ -142,6 +142,13 @@ abstract class database_driver_testcase extends base_testcase {
         try {
             parent::runBare();
 
+            // Deal with any debugging messages.
+            $debugerror = phpunit_util::display_debugging_messages(true);
+            $this->resetDebugging();
+            if (!empty($debugerror)) {
+                trigger_error('Unexpected debugging() call detected.' . "\n" . $debugerror, E_USER_NOTICE);
+            }
+
         } catch (Exception $ex) {
             $e = $ex;
         } catch (Throwable $ex) {
diff --git a/lib/phpunit/classes/util.php b/lib/phpunit/classes/util.php
index 0b0aec7eae6..1e100aa49b7 100644
--- a/lib/phpunit/classes/util.php
+++ b/lib/phpunit/classes/util.php
@@ -690,8 +690,29 @@ class phpunit_util extends testing_util {
         // we need normal debugging outside of tests to find problems in our phpunit integration.
         $backtrace = debug_backtrace();
 
+        // Only for advanced_testcase, database_driver_testcase (and descendants). Others aren't
+        // able to manage the debugging sink, so any debugging has to be output normally and, hopefully,
+        // PHPUnit execution will catch that unexpected output properly.
+        $sinksupport = false;
         foreach ($backtrace as $bt) {
-            if (isset($bt['object']) and is_object($bt['object'])
+            if (isset($bt['object']) && is_object($bt['object'])
+                && (
+                    $bt['object'] instanceof advanced_testcase ||
+                    $bt['object'] instanceof database_driver_testcase)
+            ) {
+                $sinksupport = true;
+                break;
+            }
+        }
+        if (!$sinksupport) {
+            return false;
+        }
+
+        // Verify that we are inside a PHPUnit test (little bit redundant, because
+        // we already have checked above that this is an advanced/database_driver
+        // testcase, but let's keep things double safe for now).
+        foreach ($backtrace as $bt) {
+            if (isset($bt['object']) && is_object($bt['object'])
                     && $bt['object'] instanceof PHPUnit\Framework\TestCase) {
                 $debug = new stdClass();
                 $debug->message = $message;