diff --git a/core/lib/Drupal/Core/Test/TestDatabase.php b/core/lib/Drupal/Core/Test/TestDatabase.php
index 474299276a..20cc8e6687 100644
--- a/core/lib/Drupal/Core/Test/TestDatabase.php
+++ b/core/lib/Drupal/Core/Test/TestDatabase.php
@@ -205,6 +205,8 @@ protected function getLockFile($lock_id) {
    *
    * @return int
    *   Message ID of the stored assertion.
+   *
+   * @internal
    */
   public static function insertAssert($test_id, $test_class, $status, $message = '', $group = 'Other', array $caller = []) {
     // Convert boolean status to string status.
@@ -244,6 +246,8 @@ public static function insertAssert($test_id, $test_class, $status, $message = '
    * @return array
    *   Array containing the last database prefix used and the last test class
    *   that ran.
+   *
+   * @internal
    */
   public static function lastTestGet($test_id) {
     $connection = static::getConnection();
@@ -273,6 +277,8 @@ public static function lastTestGet($test_id) {
    *
    * @return bool
    *   Whether any fatal errors were found.
+   *
+   * @internal
    */
   public function logRead($test_id, $test_class) {
     $log = DRUPAL_ROOT . '/' . $this->getTestSitePath() . '/error.log';
@@ -303,6 +309,8 @@ public function logRead($test_id, $test_class) {
    *
    * @return array
    *   Array suitable for use in a hook_schema() implementation.
+   *
+   * @internal
    */
   public static function testingSchema() {
     $schema['simpletest'] = [