Index: tests/query/results.php
===================================================================
--- tests/query/results.php	(revision 1046)
+++ tests/query/results.php	(working copy)
@@ -42,7 +42,7 @@
 		$this->factory->post->create( array( 'post_title' => 'tags-a-and-b', 'tags_input' => array( 'tag-a', 'tag-b' ), 'post_date' => '2010-08-01 00:00:00' ) );
 		$this->factory->post->create( array( 'post_title' => 'tags-b-and-c', 'tags_input' => array( 'tag-b', 'tag-c' ), 'post_date' => '2010-09-01 00:00:00' ) );
 		$this->factory->post->create( array( 'post_title' => 'tags-a-and-c', 'tags_input' => array( 'tag-a', 'tag-c' ), 'post_date' => '2010-10-01 00:00:00' ) );
-
+		
 		unset( $this->q );
 		$this->q = new WP_Query();
 	}
@@ -294,4 +294,36 @@
 		$this->assertEquals( $expected, wp_list_pluck( $posts, 'post_name' ) );
 	}
 
+	function test_query_post_parent__in() {
+		$parent_id = $this->factory->post->create( array( 'post_title' => 'parent-post' ) );
+		$child_id = $this->factory->post->create( array( 'post_title' => 'child-post', 'post_parent' => $parent_id ) );
+		
+		$posts = $this->q->query( array(  
+			'fields'          => 'ids',
+			'post_parent__in' => array( $parent_id )
+		) );
+		
+		$this->assertEquals( reset( $posts ), $child_id );
+	}
+
+	function test_order_post_parent__in() {
+		$parent_id1 = $this->factory->post->create( array( 'post_title' => rand_str() ) );
+		$parent_id2 = $this->factory->post->create( array( 'post_title' => rand_str() ) );
+		$this->factory->post->create( array( 'post_title' => rand_str(), 'post_parent' => $parent_id2 ) );
+		$this->factory->post->create( array( 'post_title' => rand_str(), 'post_parent' => $parent_id1 ) );
+		$this->factory->post->create( array( 'post_title' => rand_str(), 'post_parent' => $parent_id2 ) );
+		$this->factory->post->create( array( 'post_title' => rand_str(), 'post_parent' => $parent_id1 ) );
+		
+		$posts = $this->q->query( array(  
+			'fields'          => 'id=>parent',
+			'post_parent__in' => array( $parent_id1, $parent_id2 ),
+			'orderby'         => 'post_parent__in',
+			'order'           => 'ASC'
+		) );
+		
+		$values = array_map( 'absint', array_values( $posts ) );
+		$parents = $values;
+		sort( $parents );
+		$this->assertEquals( $parents, $values );
+	}	
 }