Correct extra dataobjects array name

tests/CommentingControllerTest.php

@@ -29,9 +29,9 @@ class CommentingControllerTest extends FunctionalTest
     /**
      * {@inheritDoc}
      */
-    protected $extraDataObjects = array(
+    protected static $extra_dataobjects = [
         CommentableItem::class
-    );
+    ];
 
     protected $securityEnabled;
 

tests/CommentsExtensionTest.php

@@ -23,7 +23,7 @@ class CommentsExtensionTest extends SapphireTest
     /**
      * {@inheritDoc}
      */
-    protected $extraDataObjects = array(
+    protected static $extra_dataobjects = array(
         CommentableItem::class,
         CommentableItemEnabled::class,
         CommentableItemDisabled::class

tests/CommentsTest.php

@@ -26,7 +26,7 @@ class CommentsTest extends FunctionalTest
 {
     protected static $fixture_file = 'comments/tests/CommentsTest.yml';
 
-    protected $extraDataObjects = array(
+    protected static $extra_dataobjects = array(
         CommentableItem::class,
         CommentableItemEnabled::class,
         CommentableItemDisabled::class

tests/Stubs/CommentableItem.php

@@ -23,6 +23,8 @@ class CommentableItem extends DataObject implements TestOnly
         CommentsExtension::class
     );
 
+    private static $table_name = 'CommentableItem';
+
     public function RelativeLink()
     {
         return 'CommentableItemController';