diff -u b/core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php b/core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php
--- b/core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php
+++ b/core/lib/Drupal/Core/DependencyInjection/Compiler/BackendCompilerPass.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\Core\DependencyInjection\Compiler;
 
-use Drupal\Core\Database\ConnectionNotDefinedException;
 use Symfony\Component\DependencyInjection\Alias;
 use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
diff -u b/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/BackendCompilerPassTest.php b/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/BackendCompilerPassTest.php
--- b/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/BackendCompilerPassTest.php
+++ b/core/tests/Drupal/Tests/Core/DependencyInjection/Compiler/BackendCompilerPassTest.php
@@ -60,32 +60,32 @@
   public function providerTestProcess() {
     $data = array();
     // Add a container with no set default_backend.
-    $prefix = __NAMESPACE__ . '\\';
-    $service = (new Definition($prefix . 'ServiceClassDefault'))->addTag('backend_overridable');
-    $container = $this->getMysqlContainer($prefix, $service);
+    $prefix = __NAMESPACE__ . '\\ServiceClass';
+    $service = (new Definition($prefix . 'Default'))->addTag('backend_overridable');
+    $container = $this->getMysqlContainer($service);
 
-    $data[] = array($prefix . 'ServiceClassDefault', $container);
+    $data[] = array($prefix . 'Default', $container);
 
     // Set the default_backend so the mysql service should be used.
-    $container = $this->getMysqlContainer($prefix, $service);
+    $container = $this->getMysqlContainer($service);
     $container->setParameter('default_backend', 'mysql');
-    $data[] = array($prefix . 'ServiceClassMysql', $container);
+    $data[] = array($prefix . 'Mysql', $container);
 
     // Configure a manual alias for the service, so ensure that it is not
     // overridden by the default backend.
     $container = clone $container;
-    $container->setDefinition('mariadb.service', new Definition($prefix . 'ServiceClassMariaDb'));
+    $container->setDefinition('mariadb.service', new Definition($prefix . 'MariaDb'));
     $container->setAlias('service', new Alias('mariadb.service'));
-    $data[] = array($prefix . 'ServiceClassMariaDb', $container);
+    $data[] = array($prefix . 'MariaDb', $container);
 
     // Check the database driver is the default.
-    $container = $this->getSqliteContainer($prefix, $service);
-    $data[] = array($prefix . 'ServiceClassSqlite', $container);
+    $container = $this->getSqliteContainer($service);
+    $data[] = array($prefix . 'Sqlite', $container);
 
     // Test the opt out.
-    $container = $this->getSqliteContainer($prefix, $service);
+    $container = $this->getSqliteContainer($service);
     $container->setParameter('default_backend', '');
-    $data[] = array($prefix . 'ServiceClassDefault', $container);
+    $data[] = array($prefix . 'Default', $container);
 
     return $data;
   }
@@ -96,14 +96,14 @@
    * This is necessary because the container clone does not clone the parameter
    * bag so the setParameter() call effects the parent container as well.
    *
-   * @param $prefix
    * @param $service
    * @return ContainerBuilder
+   * @internal param $prefix
    */
-  protected function getSqliteContainer($prefix, $service) {
+  protected function getSqliteContainer($service) {
     $container = new ContainerBuilder();
     $container->setDefinition('service', $service);
-    $container->setDefinition('sqlite.service', new Definition($prefix . 'ServiceClassSqlite'));
+    $container->setDefinition('sqlite.service', new Definition(__NAMESPACE__ . '\\ServiceClassSqlite'));
     $container->set('database', new Connection(new \PDO('sqlite::memory:'), []));
     return $container;
   }
@@ -114,14 +114,14 @@
    * This is necessary because the container clone does not clone the parameter
    * bag so the setParameter() call effects the parent container as well.
    *
-   * @param $prefix
    * @param $service
    * @return ContainerBuilder
+   * @internal param $prefix
    */
-  protected function getMysqlContainer($prefix, $service) {
+  protected function getMysqlContainer($service) {
     $container = new ContainerBuilder();
     $container->setDefinition('service', $service);
-    $container->setDefinition('mysql.service', new Definition($prefix . 'ServiceClassMysql'));
+    $container->setDefinition('mysql.service', new Definition(__NAMESPACE__ . '\\ServiceClassMysql'));
     return $container;
   }