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 fd2f42c..44b23db 100644
--- a/core/modules/file/src/Plugin/migrate/process/d6/CckFile.php
+++ b/core/modules/file/src/Plugin/migrate/process/d6/CckFile.php
@@ -50,11 +50,9 @@ 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
-    // the d6_file migration.
-    $migration_plugin_configuration = [
-      'source' => ['fid'],
-      'migration' => 'd6_file',
-    ];
+    // a d6 file migration.
+    $migration_plugin_configuration = ['source' => ['fid']] + $configuration;
+    $migration_plugin_configuration += ['migration' => 'd6_file'];
 
     return new static(
       $configuration,
@@ -100,5 +98,4 @@ public function transform($value, MigrateExecutableInterface $migrate_executable
       return [];
     }
   }
-
 }
diff --git a/core/modules/file/tests/src/Unit/Plugin/migrate/process/d6/CckFileTest.php b/core/modules/file/tests/src/Unit/Plugin/migrate/process/d6/CckFileTest.php
index 1ee73a8..929f8c2 100644
--- a/core/modules/file/tests/src/Unit/Plugin/migrate/process/d6/CckFileTest.php
+++ b/core/modules/file/tests/src/Unit/Plugin/migrate/process/d6/CckFileTest.php
@@ -3,13 +3,18 @@
 namespace Drupal\Tests\file\Unit\Plugin\migrate\process\d6;
 
 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\MigrateExecutableInterface;
 use Drupal\migrate\Plugin\MigrateProcessInterface;
+use Drupal\migrate\Plugin\MigrationPluginManager;
 use Drupal\migrate\Row;
 use Drupal\Tests\UnitTestCase;
 
 /**
+ * @coversDefaultClass \Drupal\file\Plugin\migrate\process\d6\CckFile
+ *
  * @group file
  */
 class CckFileTest extends UnitTestCase {
@@ -48,4 +53,40 @@ public function testTransformAltTitle() {
     $this->assertSame($expected, $transformed);
   }
 
+  /**
+   * Tests initialization of the iterator.
+   *
+   * @covers ::__construct
+   */
+/*  public function testConfigurableFileMigration() {
+    $migration = $this->prophesize(MigrationInterface::class)->reveal();
+    $migration_plugin = $this->prophesize(MigrateProcessInterface::class);
+
+    $migrationPluginManager = $this->getMockClass(MigrationPluginManager::class, ['createInstance']);
+    $migrationProcessPlugin = $this->prophesize(TestableMigration::class);
+    $migrationPluginManager::staticExpects
+    $migrationPluginManager->createInstance()->willReturn($migrationProcessPlugin);
+    $testableMigration = new CckFile(['migration' => 'custom_file'], 'custom_file', [], $migration, $migration_plugin->reveal());
+
+    $this->assertEquals('custom_file', $migrationProcessPlugin->getConfiguration()['migration']);
+  }*/
+
+}
+
+/**
+ * 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;
+  }
 }