diff -u b/core/modules/node/src/Tests/Migrate/d6/MigrateNodeTest.php b/core/modules/node/src/Tests/Migrate/d6/MigrateNodeTest.php
--- b/core/modules/node/src/Tests/Migrate/d6/MigrateNodeTest.php
+++ b/core/modules/node/src/Tests/Migrate/d6/MigrateNodeTest.php
@@ -62,6 +62,8 @@
     $this->assertIdentical('Drupal Groups', $node->field_test_link->title);
     $this->assertIdentical([], $node->field_test_link->options['attributes']);
 
+    // Rerun migration with invalid link attributes and a different URL and
+    // title. If only the attributes are changed the error does not occur.
     Database::getConnection('default', 'migrate')
       ->update('content_type_story')
       ->fields([