diff --git a/core/tests/Drupal/KernelTests/KernelTestBaseTest.php b/core/tests/Drupal/KernelTests/KernelTestBaseTest.php
index ae0da56..f4e351b 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBaseTest.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBaseTest.php
@@ -90,8 +90,10 @@ public function testSetUp() {
     $schema = $this->container->get('database')->schema();
     $schema->createTable('foo', array(
       'fields' => array(
-        'name' => array(
-          'type' => 'varchar',
+        'number' => array(
+          'type' => 'int',
+          'unsigned' => TRUE,
+          'not null' => TRUE,
         ),
       ),
     ));
@@ -105,9 +107,9 @@ public function testSetUp() {
   public function testSetUpDoesNotLeak() {
     $this->assertArrayNotHasKey('destroy-me', $GLOBALS);
 
-    $expected = [];
+    // Ensure that we have a different database prefix.
     $schema = $this->container->get('database')->schema();
-    $this->assertEquals($expected, $schema->findTables('%'));
+    $this->assertFalse($schema->tableExists('foo'));
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/KernelTestBase.php b/core/tests/Drupal/Tests/KernelTestBase.php
index 76b25bb..a5504d0 100644
--- a/core/tests/Drupal/Tests/KernelTestBase.php
+++ b/core/tests/Drupal/Tests/KernelTestBase.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Tests;
 
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Component\Utility\String;
 use Drupal\Core\Config\ConfigImporter;
 use Drupal\Core\Config\StorageComparer;
@@ -15,12 +16,9 @@
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\DependencyInjection\ServiceProviderInterface;
 use Drupal\Core\DrupalKernel;
-use Drupal\Core\Entity\Schema\EntitySchemaProviderInterface;
 use Drupal\Core\Entity\Sql\SqlEntityStorageInterface;
 use Drupal\Core\Extension\ExtensionDiscovery;
-use Drupal\Core\Logger\RfcLogLevel;
 use Drupal\Core\Site\Settings;
-use Drupal\Core\StreamWrapper\StreamWrapperInterface;
 use Drupal\simpletest\AssertContentTrait;
 use Drupal\simpletest\RandomGeneratorTrait;
 use Psr\Log\LoggerInterface;
@@ -756,7 +754,7 @@ protected function installEntitySchema($entity_type_id) {
       $all_tables_exist = TRUE;
       foreach ($tables as $table) {
         if (!$db_schema->tableExists($table)) {
-          $this->fail(String::format('Installed entity type table for the %entity_type entity type: %table', array(
+          $this->fail(SafeMarkup::format('Installed entity type table for the %entity_type entity type: %table', array(
             '%entity_type' => $entity_type_id,
             '%table' => $table,
           )));
@@ -764,7 +762,7 @@ protected function installEntitySchema($entity_type_id) {
         }
       }
       if ($all_tables_exist) {
-        $this->pass(String::format('Installed entity type tables for the %entity_type entity type: %tables', array(
+        $this->pass(SafeMarkup::format('Installed entity type tables for the %entity_type entity type: %tables', array(
           '%entity_type' => $entity_type_id,
           '%tables' => '{' . implode('}, {', $tables) . '}',
         )));
@@ -886,7 +884,7 @@ protected function render(array &$elements) {
     $content = $this->container->get('renderer')->render($elements);
     drupal_process_attached($elements);
     $this->setRawContent($content);
-    $this->verbose('<pre style="white-space: pre-wrap">' . String::checkPlain($content));
+    $this->verbose('<pre style="white-space: pre-wrap">' . SafeMarkup::checkPlain($content));
     return $content;
   }