reverted:
--- b/core/modules/book/src/Tests/d6/MigrateBookConfigsTest.php
+++ a/core/modules/migrate_drupal/src/Tests/d6/MigrateBookConfigsTest.php
@@ -2,18 +2,17 @@
 
 /**
  * @file
+ * Contains \Drupal\migrate_drupal\Tests\d6\MigrateBookConfigsTest.
- * Contains \Drupal\book\Tests\d6\MigrateBookConfigsTest.
  */
 
+namespace Drupal\migrate_drupal\Tests\d6;
-namespace Drupal\book\Tests\d6;
 
 use Drupal\config\Tests\SchemaCheckTestTrait;
-use Drupal\migrate_drupal\Tests\d6\MigrateDrupal6TestBase;
 
 /**
  * Upgrade variables to book.settings.yml.
  *
+ * @group migrate_drupal
- * @group book
  */
 class MigrateBookConfigsTest extends MigrateDrupal6TestBase {
 
reverted:
--- b/core/modules/book/src/Tests/d6/MigrateBookTest.php
+++ a/core/modules/migrate_drupal/src/Tests/d6/MigrateBookTest.php
@@ -2,18 +2,17 @@
 
 /**
  * @file
+ * Contains \Drupal\migrate_drupal\Tests\d6\MigrateBookTest.
- * Contains \Drupal\book\Tests\d6\MigrateBookTest.
  */
 
+namespace Drupal\migrate_drupal\Tests\d6;
-namespace Drupal\book\Tests\d6;
 
-use Drupal\migrate_drupal\Tests\d6\MigrateDrupal6TestBase;
 use Drupal\node\Entity\Node;
 
 /**
  * Upgrade book structure.
  *
+ * @group migrate_drupal
- * @group book
  */
 class MigrateBookTest extends MigrateDrupal6TestBase {
 
only in patch2:
unchanged:
--- a/core/modules/migrate/src/Plugin/migrate/destination/Book.php
+++ b/core/modules/book/src/Plugin/migrate/destination/Book.php
@@ -2,12 +2,13 @@
 
 /**
  * @file
- * Contains \Drupal\migrate\Plugin\migrate\destination\Book.
+ * Contains \Drupal\book\Plugin\migrate\destination\Book.
  */
 
-namespace Drupal\migrate\Plugin\migrate\destination;
+namespace Drupal\book\Plugin\migrate\destination;
 
 use Drupal\Core\Entity\EntityInterface;
+use Drupal\migrate\Plugin\migrate\destination\EntityContentBase;
 use Drupal\migrate\Row;
 
 /**
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/src/Tests/d6/MigrateBookConfigsTest.php
+++ b/core/modules/book/src/Tests/Migrate/d6/MigrateBookConfigsTest.php
@@ -2,17 +2,18 @@
 
 /**
  * @file
- * Contains \Drupal\migrate_drupal\Tests\d6\MigrateBookConfigsTest.
+ * Contains \Drupal\book\Tests\Migrate\d6\MigrateBookConfigsTest.
  */
 
-namespace Drupal\migrate_drupal\Tests\d6;
+namespace Drupal\book\Tests\Migate\d6;
 
 use Drupal\config\Tests\SchemaCheckTestTrait;
+use Drupal\migrate_drupal\Tests\d6\MigrateDrupal6TestBase;
 
 /**
  * Upgrade variables to book.settings.yml.
  *
- * @group migrate_drupal
+ * @group book
  */
 class MigrateBookConfigsTest extends MigrateDrupal6TestBase {
 
only in patch2:
unchanged:
--- a/core/modules/migrate_drupal/src/Tests/d6/MigrateBookTest.php
+++ b/core/modules/book/src/Tests/Migrate/d6/MigrateBookTest.php
@@ -2,17 +2,18 @@
 
 /**
  * @file
- * Contains \Drupal\migrate_drupal\Tests\d6\MigrateBookTest.
+ * Contains \Drupal\book\Tests\Migrate\d6\MigrateBookTest.
  */
 
-namespace Drupal\migrate_drupal\Tests\d6;
+namespace Drupal\book\Tests\Migrate\d6;
 
+use Drupal\migrate_drupal\Tests\d6\MigrateDrupal6TestBase;
 use Drupal\node\Entity\Node;
 
 /**
  * Upgrade book structure.
  *
- * @group migrate_drupal
+ * @group book
  */
 class MigrateBookTest extends MigrateDrupal6TestBase {