diff --git a/core/modules/file/src/Plugin/migrate/process/d6/CckFile.php b/core/modules/file/src/Plugin/migrate/process/d6/CckFile.php
index 44b23db..748eff0 100644
--- a/core/modules/file/src/Plugin/migrate/process/d6/CckFile.php
+++ b/core/modules/file/src/Plugin/migrate/process/d6/CckFile.php
@@ -51,8 +51,10 @@ public function __construct(array $configuration, $plugin_id, $plugin_definition
   public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration = NULL) {
     // Configure the migration process plugin to look up migrated IDs from
     // a d6 file migration.
-    $migration_plugin_configuration = ['source' => ['fid']] + $configuration;
-    $migration_plugin_configuration += ['migration' => 'd6_file'];
+    $migration_plugin_configuration = $configuration + [
+      'migration' => 'd6_file',
+      'source' => ['fid'],
+    ];
 
     return new static(
       $configuration,
diff --git a/core/modules/file/tests/src/Kernel/Migrate/process/d6/CckFileTest.php b/core/modules/file/tests/src/Kernel/Migrate/process/d6/CckFileTest.php
index 120a22c..1c60c95 100644
--- a/core/modules/file/tests/src/Kernel/Migrate/process/d6/CckFileTest.php
+++ b/core/modules/file/tests/src/Kernel/Migrate/process/d6/CckFileTest.php
@@ -1,13 +1,9 @@
 <?php
 
-namespace Drupal\Tests\file\Kernel\Migrate\d6;
+namespace Drupal\Tests\file\Kernel\Migrate\process\d6;
 
-use Drupal\Core\Cache\CacheBackendInterface;
-use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\file\Plugin\migrate\process\d6\CckFile;
-use Drupal\migrate\Plugin\migrate\process\Migration;
-use Drupal\migrate\Plugin\MigratePluginManager;
-use Drupal\migrate\Plugin\MigrationInterface;
+use Drupal\migrate\Plugin\Migration;
 use Drupal\Tests\migrate_drupal\Kernel\MigrateDrupalTestBase;
 
 /**
@@ -15,9 +11,9 @@
  *
  * @coversDefaultClass \Drupal\file\Plugin\migrate\process\d6\CckFile
  *
- * @group migrate_drupal_6
+ * @group file
  */
-class MigrateCckFileTest extends MigrateDrupalTestBase {
+class CckFileTest extends MigrateDrupalTestBase {
 
   /**
    * Tests configurability of file migration name.
@@ -25,62 +21,12 @@ class MigrateCckFileTest extends MigrateDrupalTestBase {
    * @covers ::__construct
    */
   public function testConfigurableFileMigration() {
-    $migration = $this->prophesize(MigrationInterface::class)->reveal();
-    $cache = $this->prophesize(CacheBackendInterface::class)->reveal();
-    $moduleHandler = $this->prophesize(ModuleHandlerInterface::class)->reveal();
-    $migrationPluginManager = new TestableMigratePluginManager('process', new \ArrayObject(), $cache, $moduleHandler);
-    $this->container->set('plugin.manager.migrate.process', $migrationPluginManager);
-    $testableMigration = TestableCckFile::create($this->container, ['migration' => 'custom_file'], 'custom_file', [], $migration);
+    $migration = Migration::create($this->container, [], 'custom_migration', []);
+    $cck_file_migration = CckFile::create($this->container, ['migration' => 'custom_file'], 'custom_file', [], $migration);
+    $migration_plugin = $this->readAttribute($cck_file_migration, 'migrationPlugin');
+    $config = $this->readAttribute($migration_plugin, 'configuration');
 
-    $this->assertEquals('custom_file', $testableMigration->getMigrationPlugin()->getConfiguration()['migration']);
-  }
-
-}
-
-/**
- * Class TestableMigration
- *
- * Provide a means to test the cck file migration.
- */
-class TestableCckFile extends CckFile {
-
-  /**
-   * Return the migration process plugin.
-   *
-   * @return array
-   *   The migration process plugin.
-   */
-  public function getMigrationPlugin() {
-    return $this->migrationPlugin;
-  }
-}
-
-/**
- * Class TestableMigration
- *
- * Provide a means to test the cck file migration.
- */
-class TestableMigration extends Migration {
-
-  /**
-   * Return the migration process plugin.
-   *
-   * @return array
-   *   The configuration for the migration process plugin.
-   */
-  public function getConfiguration() {
-    return $this->configuration;
-  }
-}
-
-/**
- * Class TestableMigratePluginManager
- *
- * Provides a means to provide a testable migration process plugin.
- */
-class TestableMigratePluginManager extends MigratePluginManager {
-  public function createInstance($pluginId, array $configuration = [], MigrationInterface $migration = NULL) {
-    return TestableMigration::create(\Drupal::getContainer(), $configuration, $pluginId, [], $migration);
+    $this->assertEquals($config['migration'], 'custom_file');
   }
 
 }