diff --git a/core/lib/Drupal/Core/Test/TestUpdateRegistry.php b/core/lib/Drupal/Core/Test/TestUpdateRegistry.php
index a62b12d..841f707 100644
--- a/core/lib/Drupal/Core/Test/TestUpdateRegistry.php
+++ b/core/lib/Drupal/Core/Test/TestUpdateRegistry.php
@@ -1,13 +1,15 @@
 <?php
 
-namespace Drupal\Core\Update;
+namespace Drupal\Core\Test;
+
+use Drupal\Core\Update\UpdateRegistry;
 
 /**
  * UpdateRegistryTest used for tests.
  *
  * @see UpdateRegistry
  */
-class UpdateRegistryTest {
+class TestUpdateRegistry extends UpdateRegistry {
 
   /**
    * {@inheritdoc}
diff --git a/core/modules/system/src/SystemConfigSubscriber.php b/core/modules/system/src/SystemConfigSubscriber.php
index acebf14..f5df073 100644
--- a/core/modules/system/src/SystemConfigSubscriber.php
+++ b/core/modules/system/src/SystemConfigSubscriber.php
@@ -153,7 +153,7 @@ public static function getSubscribedEvents() {
     // there is no configuration to import.
     $events[ConfigEvents::IMPORT_VALIDATE][] = ['onConfigImporterValidateNotEmpty', 512];
     $events[ConfigEvents::IMPORT_VALIDATE][] = ['onConfigImporterValidateSiteUUID', 256];
-    $events[ConfigEvents::IMPORT_VALIDATE][] = ['onConfigImporterValidateDatabaseUpdate', 255];
+    $events[ConfigEvents::IMPORT_VALIDATE][] = ['onConfigImporterValidateDatabaseUpdate', 128];
     return $events;
   }
 
diff --git a/core/modules/system/src/Tests/Update/UpdatePendingConfigImportTest.php b/core/modules/system/src/Tests/Update/UpdatePendingConfigImportTest.php
index 4047991..c43bd94 100644
--- a/core/modules/system/src/Tests/Update/UpdatePendingConfigImportTest.php
+++ b/core/modules/system/src/Tests/Update/UpdatePendingConfigImportTest.php
@@ -47,13 +47,13 @@ public function testConfigImport() {
     try {
       // Try running config import with pending.
       $this->configImporter()->import();
+      $error_log = [];
     }
     catch (ConfigImporterException $e) {
       $this->assertEqual($e->getMessage(), 'There were errors validating the config synchronization.');
       $error_log = $this->configImporter->getErrors();
-      $expected = array('Pending database updates available.');
-      $this->assertEqual($expected, $error_log);
     }
+    $this->assertEqual(['Pending database updates available.'], $error_log);
 
     // Run database updates.
     $this->runUpdates();
diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index 766cc4f..45d0256 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -17,6 +17,7 @@
 use Drupal\Core\Language\Language;
 use Drupal\Core\Site\Settings;
 use Drupal\Core\Test\TestDatabase;
+use Drupal\Core\Test\TestUpdateRegistry;
 use Drupal\simpletest\AssertContentTrait;
 use Drupal\simpletest\AssertHelperTrait;
 use Drupal\Tests\ConfigTestTrait;
@@ -618,7 +619,7 @@ public function register(ContainerBuilder $container) {
 
     // We don't care about post updates in the kernel test base.
     $container->removeDefinition('update.post_update_registry');
-    $container->register('update.post_update_registry', 'Drupal\Core\Update\UpdateRegistryTest');
+    $container->register('update.post_update_registry', TestUpdateRegistry::class);
 
     if ($container->hasDefinition('path_processor_alias')) {
       // Prevent the alias-based path processor, which requires a url_alias db
@@ -812,7 +813,7 @@ protected function installSchema($module, $tables) {
 
       // Set a very high schema version so no updates are found because we
       // don't want to run them anyway.
-      drupal_set_installed_schema_version($module, 8888);
+      drupal_set_installed_schema_version($module, PHP_INT_MAX);
     }
   }