Update to Drupal 8.0.0-beta15. For more information, see: https://www.drupal.org/node/2563023

core/modules/taxonomy/tests/src/Unit/Migrate/d6/TermTestBase.php

@@ -19,7 +19,6 @@ abstract class TermTestBase extends MigrateSqlSourceTestCase {
   protected $migrationConfiguration = array(
     'id' => 'test',
     'highWaterProperty' => array('field' => 'test'),
-    'idlist' => array(),
     'source' => array(
       'plugin' => 'd6_taxonomy_term',
     ),

core/modules/taxonomy/tests/src/Unit/Migrate/d6/VocabularyTest.php

@@ -22,8 +22,6 @@ class VocabularyTest extends MigrateSqlSourceTestCase {
   protected $migrationConfiguration = [
     // The ID of the entity, can be any string.
     'id' => 'test',
-    // Leave it empty for now.
-    'idlist' => [],
     'source' => [
       'plugin' => 'd6_vocabulary',
     ],