Post-initial commit

13 files changed, 655 insertions, 82 deletions

diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..4b66fcb
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,339 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc., <http://fsf.org/>
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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+
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+                            NO WARRANTY
+
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+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    {description}
+    Copyright (C) 2020  Daniel Weipert
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  {signature of Ty Coon}, 1 April 1989
+  Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.
diff --git a/Readme.md b/Readme.md
new file mode 100644
index 0000000..1f95cd8
--- /dev/null
+++ b/Readme.md
@@ -0,0 +1,17 @@
+# Draggable Post Order
+
+## Features
+
+- makes post types orderable in the admin screen via drag'n'drop with *jquery-ui-sortable*
+
+## How to use
+
+Add this to your **functions.php**
+
+```php
+add_post_type_support('your-custom-post-type', \Draggable_Post_Order\Draggable_Post_Order::$post_type_feature);
+```
+
+## License
+
+[GPL v2](LICENSE)
diff --git a/composer.json b/composer.json
index e2628ee..a3c1e6c 100644
--- a/composer.json
+++ b/composer.json
@@ -2,6 +2,7 @@
     "name": "drogueronin/draggable-post-order",
     "version": "1.0.0",
     "type": "wordpress-plugin",
+    "license": "GPL-2.0-or-later",
     "authors": [
         {
             "name": "Daniel Weipert",
@@ -31,9 +32,9 @@
         "exclude": [
             "*", ".*",
             "!/build",
+            "!/languages",
             "!/src",
             "!/vendor",
-            "!/composer.json",
             "!/draggable-post-order.php",
             "!/LICENSE", "!/readme.txt"
         ]
diff --git a/draggable-post-order.php b/draggable-post-order.php
index 80abf34..026b1c1 100644
--- a/draggable-post-order.php
+++ b/draggable-post-order.php
@@ -19,7 +19,7 @@
 require __DIR__ . '/vendor/autoload.php';
 
 /**
- * Callback for "init" action
+ * Callback for "init" action.
  */
 function draggable_post_order() {
 	\Draggable_Post_Order\Draggable_Post_Order::init();
@@ -27,7 +27,7 @@ function draggable_post_order() {
 add_action( 'init', 'draggable_post_order' );
 
 /**
- * URL to enqueue scripts and styles
+ * URL to enqueue scripts and styles.
  *
  * @param string $path Relative path inside the build folder.
  *
@@ -38,7 +38,7 @@ function draggable_post_order_assets_url( $path ) {
 }
 
 /**
- * Absolute path to plugin folder
+ * Absolute path to plugin folder.
  *
  * @return string
  */
diff --git a/languages/draggable-post-order-de_DE.po b/languages/draggable-post-order-de_DE.po
deleted file mode 100644
index d7f4055..0000000
--- a/languages/draggable-post-order-de_DE.po
+++ /dev/null
@@ -1,42 +0,0 @@
-# Copyright (C) 2020 Daniel Weipert
-# This file is distributed under the same license as the Draggable Post Order plugin.
-msgid ""
-msgstr ""
-"Project-Id-Version: Draggable Post Order 1.0.0\n"
-"Report-Msgid-Bugs-To: https://wordpress.org/support/plugin/draggable-post-"
-"order\n"
-"Language-Team: \n"
-"MIME-Version: 1.0\n"
-"Content-Type: text/plain; charset=UTF-8\n"
-"Content-Transfer-Encoding: 8bit\n"
-"POT-Creation-Date: 2020-12-21T14:13:39+00:00\n"
-"PO-Revision-Date: 2020-12-21 15:28+0100\n"
-"X-Generator: Poedit 2.4.2\n"
-"X-Domain: draggable-post-order\n"
-"Last-Translator: \n"
-"Plural-Forms: nplurals=2; plural=(n != 1);\n"
-"Language: de\n"
-
-#. Plugin Name of the plugin
-msgid "Draggable Post Order"
-msgstr "Draggable Post Order"
-
-#. Plugin URI of the plugin
-msgid "https://gitlab.com/DRogueRonin/wp-plugin-draggable-post-order"
-msgstr "https://gitlab.com/DRogueRonin/wp-plugin-draggable-post-order"
-
-#. Description of the plugin
-msgid "Drag'n'drop posts to order them"
-msgstr "Beiträge per Drag’n’drop sortieren"
-
-#. Author of the plugin
-msgid "Daniel Weipert"
-msgstr "Daniel Weipert"
-
-#. Author URI of the plugin
-msgid "https://dweipert.de"
-msgstr "https://dweipert.de"
-
-#: src/class-draggable-post-order.php:90
-msgid "Post Order"
-msgstr "Beitragsreihenfolge"
diff --git a/languages/draggable-post-order.pot b/languages/draggable-post-order.pot
index da47b47..ef4a7cc 100644
--- a/languages/draggable-post-order.pot
+++ b/languages/draggable-post-order.pot
@@ -9,7 +9,7 @@ msgstr ""
 "MIME-Version: 1.0\n"
 "Content-Type: text/plain; charset=UTF-8\n"
 "Content-Transfer-Encoding: 8bit\n"
-"POT-Creation-Date: 2020-12-21T14:13:39+00:00\n"
+"POT-Creation-Date: 2020-12-24T13:18:15+00:00\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "X-Generator: WP-CLI 2.4.0\n"
 "X-Domain: draggable-post-order\n"
@@ -34,6 +34,6 @@ msgstr ""
 msgid "https://dweipert.de"
 msgstr ""
 
-#: src/class-draggable-post-order.php:90
+#: src/class-draggable-post-order.php:114
 msgid "Post Order"
 msgstr ""
diff --git a/package.json b/package.json
index 4ebd44c..78133a6 100644
--- a/package.json
+++ b/package.json
@@ -1,30 +1,27 @@
 {
   "name": "draggable-post-order",
   "version": "1.0.0",
-  "description": "",
-  "author": "",
-  "license": "MIT",
-  "keywords": [],
-  "homepage": "",
-  "repository": "",
-  "bugs": "",
-  "main": "index.js",
+  "description": "Drag'n'drop posts to order them",
+  "author": "Daniel Weipert <code@drogueronin.de>",
+  "license": "GPL-2.0-or-later",
+  "keywords": [
+    "post-type", "custom-post-type", "order", "drag"
+  ],
+  "homepage": "https://gitlab.com/DRogueRonin/wp-plugin-draggable-post-order",
+  "repository": "https://gitlab.com/DRogueRonin/wp-plugin-draggable-post-order",
+  "bugs": "https://gitlab.com/DRogueRonin/wp-plugin-draggable-post-order",
+  "main": "src/index.js",
   "devDependencies": {
     "@wordpress/scripts": "^12.6.0"
   },
   "scripts": {
     "build": "wp-scripts build",
-    "check-engines": "wp-scripts check-engines",
-    "check-licenses": "wp-scripts check-licenses",
+    "start": "wp-scripts start",
     "format:js": "wp-scripts format-js src",
-    "lint:css": "wp-scripts lint-style src",
+    "format:css": "wp-scripts lint-style src -- --fix",
     "lint:js": "wp-scripts lint-js src",
-    "lint:md:docs": "wp-scripts lint-md-docs",
-    "lint:md:js": "wp-scripts lint-md-js",
+    "lint:css": "wp-scripts lint-style src",
     "lint:pkg-json": "wp-scripts lint-pkg-json",
-    "packages-update": "wp-scripts packages-update",
-    "start": "wp-scripts start",
-    "test:e2e": "wp-scripts test-e2e",
-    "test:unit": "wp-scripts test-unit-js"
+    "packages-update": "wp-scripts packages-update"
   }
 }
diff --git a/readme.txt b/readme.txt
new file mode 100644
index 0000000..69ed5d6
--- /dev/null
+++ b/readme.txt
@@ -0,0 +1,25 @@
+=== Draggable Post Order ===
+Contributors: drogueronin
+Tags: post-type, custom-post-type, order, drag
+Requires at least: 5.5
+Tested up to: 5.6
+Stable tag: 1.0.0
+Requires PHP: 7.4
+License: GPLv2 or later
+License URI: https://www.gnu.org/licenses/gpl-2.0.html
+
+Drag'n'drop posts to order them
+
+== Description ==
+
+### Features
+
+- makes post types orderable in the admin screen via drag'n'drop with *jquery-ui-sortable*
+
+### How to use
+
+Add this to your **functions.php**
+
+`
+add_post_type_support('your-custom-post-type', \Draggable_Post_Order\Draggable_Post_Order::$post_type_feature);
+`
diff --git a/src/class-adjacent-post-order.php b/src/class-adjacent-post-order.php
new file mode 100644
index 0000000..3517696
--- /dev/null
+++ b/src/class-adjacent-post-order.php
@@ -0,0 +1,124 @@
+<?php
+/**
+ * Functions for getting the correct adjacent post
+ *
+ * @package Draggable_Post_Order
+ */
+
+namespace Draggable_Post_Order;
+
+/**
+ * Class Adjacent_Post_Order
+ *
+ * @package Draggable_Post_Order
+ */
+class Adjacent_Post_Order {
+
+	/**
+	 * Initialize.
+	 */
+	public static function init() {
+		add_filter( 'get_previous_post_join', [ self::class, 'get_post_join' ], 10, 5 );
+		add_filter( 'get_next_post_join', [ self::class, 'get_post_join' ], 10, 5 );
+		add_filter( 'get_previous_post_where', [ self::class, 'get_previous_post_where' ], 10, 5 );
+		add_filter( 'get_next_post_where', [ self::class, 'get_next_post_where' ], 10, 5 );
+		add_filter( 'get_previous_post_sort', [ self::class, 'get_post_sort' ], 10, 3 );
+		add_filter( 'get_next_post_sort', [ self::class, 'get_post_sort' ], 10, 3 );
+	}
+
+	/**
+	 * Callback for "get_previous_post_join" and "get_previous_post_join" filters.
+	 * Joins in the postmeta table for further use.
+	 *
+	 * @param string  $join           The JOIN clause in the SQL.
+	 * @param bool    $in_same_term   Whether post should be in a same taxonomy term.
+	 * @param array   $excluded_terms Array of excluded term IDs.
+	 * @param string  $taxonomy       Taxonomy. Used to identify the term used when `$in_same_term` is true.
+	 * @param WP_Post $post           WP_Post object.
+	 *
+	 * @return string
+	 */
+	public static function get_post_join( $join, $in_same_term, $excluded_terms, $taxonomy, $post ) {
+		if ( ! Draggable_Post_Order::supports( $post->post_type ) ) {
+			return $join;
+		}
+
+		global $wpdb;
+
+		$join .= " INNER JOIN {$wpdb->postmeta} as pm ON p.id = pm.post_id";
+
+		return $join;
+	}
+
+	/**
+	 * Helper function to set the WHERE clause.
+	 *
+	 * @param string  $where The `WHERE` clause in the SQL.
+	 * @param WP_Post $post  WP_Post object.
+	 * @param string  $op    The comparative operator to use.
+	 *
+	 * @return string
+	 */
+	private static function get_post_where( $where, $post, $op ) {
+		if ( ! Draggable_Post_Order::supports( $post->post_type ) ) {
+			return $where;
+		}
+
+		global $wpdb;
+
+		$post_order = get_post_meta( $post->ID, Draggable_Post_Order::$meta_key, true );
+
+		return $wpdb->prepare(
+		    // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
+			"WHERE pm.meta_key = %s AND pm.meta_value $op %s AND p.post_type = %s AND p.post_status = 'publish'",
+			Draggable_Post_Order::$meta_key,
+			$post_order,
+			$post->post_type
+		);
+	}
+
+	/**
+	 * Callback for "get_previous_post_where" filter.
+	 *
+	 * @param string  $where          The `WHERE` clause in the SQL.
+	 * @param bool    $in_same_term   Whether post should be in a same taxonomy term.
+	 * @param array   $excluded_terms Array of excluded term IDs.
+	 * @param string  $taxonomy       Taxonomy. Used to identify the term used when `$in_same_term` is true.
+	 * @param WP_Post $post           WP_Post object.
+	 * @return string
+	 */
+	public static function get_previous_post_where( $where, $in_same_term, $excluded_terms, $taxonomy, $post ) {
+		return self::get_post_where( $where, $post, '<' );
+	}
+
+	/**
+	 * Callback for "get_next_post_where" filter.
+	 *
+	 * @param string  $where          The `WHERE` clause in the SQL.
+	 * @param bool    $in_same_term   Whether post should be in a same taxonomy term.
+	 * @param array   $excluded_terms Array of excluded term IDs.
+	 * @param string  $taxonomy       Taxonomy. Used to identify the term used when `$in_same_term` is true.
+	 * @param WP_Post $post           WP_Post object.
+	 * @return string
+	 */
+	public static function get_next_post_where( $where, $in_same_term, $excluded_terms, $taxonomy, $post ) {
+		return self::get_post_where( $where, $post, '>' );
+	}
+
+	/**
+	 * Callback for "get_previous_post_sort" and "get_next_post_sort" filters.
+	 *
+	 * @param string  $order_by The `ORDER BY` clause in the SQL.
+	 * @param WP_Post $post    WP_Post object.
+	 * @param string  $order   Sort order. 'DESC' for previous post, 'ASC' for next.
+	 *
+	 * @return string
+	 */
+	public static function get_post_sort( $order_by, $post, $order ) {
+		if ( ! Draggable_Post_Order::supports( $post->post_type ) ) {
+			return $order_by;
+		}
+
+		return "ORDER BY pm.meta_value $order LIMIT 1";
+	}
+}
diff --git a/src/class-draggable-post-order.php b/src/class-draggable-post-order.php
index ae9b501..a976816 100644
--- a/src/class-draggable-post-order.php
+++ b/src/class-draggable-post-order.php
@@ -15,10 +15,31 @@ namespace Draggable_Post_Order;
 class Draggable_Post_Order {
 
 	/**
+	 * The meta key.
+	 *
+	 * @var string
+	 */
+	public static string $meta_key = 'draggable-post-order';
+
+	/**
+	 * The post type feature.
+	 *
+	 * @var string
+	 */
+	public static string $post_type_feature = 'draggable-post-order';
+
+	/**
+	 * The nonce name.
+	 *
+	 * @var string
+	 */
+	public static string $nonce = 'draggable-post-order';
+
+	/**
 	 * Initialize.
 	 */
 	public static function init() {
-		$post_types = get_post_types_by_support( 'draggable-post-order' );
+		$post_types = get_post_types_by_support( self::$post_type_feature );
 
 		// if there are no post types to order => return.
 		if ( empty( $post_types ) ) {
@@ -40,6 +61,9 @@ class Draggable_Post_Order {
 
 		// sort posts by post order.
 		add_action( 'pre_get_posts', [ self::class, 'order_posts' ] );
+
+		// sort for adjacent posts.
+		Adjacent_Post_Order::init();
 	}
 
 	/**
@@ -52,7 +76,7 @@ class Draggable_Post_Order {
 	public static function supports( $post_type = null ) {
 		$post_type ??= get_current_screen()->post_type ?? '';
 
-		return post_type_supports( $post_type, 'draggable-post-order' );
+		return post_type_supports( $post_type, self::$post_type_feature );
 	}
 
 	/**
@@ -64,19 +88,19 @@ class Draggable_Post_Order {
 	public static function save_post( $post_id, $post ) {
 		if (
 			( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) ||
-			! check_admin_referer( 'metaBoxDraggablePostOrder', 'metaBoxDraggablePostOrder' ) ||
+			! check_admin_referer( self::$nonce, self::$nonce ) ||
 			( ! isset( $_POST['post_ID'] ) || intval( $_POST['post_ID'] ) !== intval( $post_id ) ) ||
-			! isset( $_POST['draggable-post-order'] )
+			! isset( $_POST[ self::$meta_key ] )
 		) {
 			return;
 		}
 
-		$post_order = sanitize_text_field( wp_unslash( $_POST['draggable-post-order'] ) );
+		$post_order = sanitize_text_field( wp_unslash( $_POST[ self::$meta_key ] ) );
 		if ( empty( $post_order ) ) {
 			$post_order = wp_count_posts( $post->post_type )->publish;
 		}
 
-		update_post_meta( $post_id, 'draggable-post-order', $post_order );
+		update_post_meta( $post_id, self::$meta_key, $post_order );
 	}
 
 	/**
@@ -96,8 +120,8 @@ class Draggable_Post_Order {
 	 * @param \WP_Post $post The post object.
 	 */
 	public static function add_meta_box( $post ) {
-		wp_nonce_field( 'metaBoxDraggablePostOrder', 'metaBoxDraggablePostOrder' );
-		?><input type="number" name="draggable-post-order" value="<?php echo get_post_meta( $post->ID, 'draggable-post-order', true ); ?>">
+		wp_nonce_field( self::$nonce, self::$nonce );
+		?><input type="number" name="<?php echo esc_html( self::$meta_key ); ?>" value="<?php echo esc_html( get_post_meta( $post->ID, self::$meta_key, true ) ); ?>">
 		<?php
 	}
 
@@ -105,17 +129,19 @@ class Draggable_Post_Order {
 	 * Callback for "wp_ajax" action.
 	 */
 	public static function update_post_order() {
-		if ( ! isset( $_POST['page'] ) || ! isset( $_POST['perPage'] ) || ! isset( $_POST['postOrder'] ) ) {
+		if ( ! check_ajax_referer( self::$nonce, 'nonce' ) ||
+			! isset( $_POST['page'] ) || ! isset( $_POST['perPage'] ) || ! isset( $_POST['postOrder'] ) ) {
 			return;
 		}
 
 		$page     = intval( $_POST['page'] );
 		$per_page = intval( $_POST['perPage'] );
+        //phpcs:ignore WordPress.Security.ValidatedSanitizedInput.MissingUnslash, WordPress.Security.ValidatedSanitizedInput.InputNotSanitized
 		parse_str( $_POST['postOrder'], $post_order );
 
 		foreach ( $post_order['post'] as $order => $post_id ) {
 			$order = intval( $order ) + 1;
-			update_post_meta( $post_id, 'draggable-post-order', ( ( $page - 1 ) * $per_page ) + $order );
+			update_post_meta( $post_id, self::$meta_key, ( ( $page - 1 ) * $per_page ) + $order );
 		}
 	}
 
@@ -132,6 +158,13 @@ class Draggable_Post_Order {
 		$dependencies[] = 'jquery-ui-sortable';
 		wp_enqueue_script( 'draggable-post-order', draggable_post_order_assets_url( 'index.js' ), $dependencies, $version, true );
 		wp_enqueue_style( 'draggable-post-order', draggable_post_order_assets_url( 'index.css' ), [], $version );
+		wp_localize_script(
+			'draggable-post-order',
+			'draggablePostOrder',
+			[
+				'nonce' => wp_create_nonce( self::$nonce ),
+			]
+		);
 	}
 
 	/**
@@ -150,12 +183,12 @@ class Draggable_Post_Order {
 			$meta_sub_query = [
 				'relation'                           => 'OR',
 				'draggable-post-order-clause'        => [
-					'key'  => 'draggable-post-order',
+					'key'  => self::$meta_key,
 					'type' => 'NUMERIC',
 				],
 				// get all posts without the meta as well.
 				'draggable-post-order-exists-clause' => [
-					'key'     => 'draggable-post-order',
+					'key'     => self::$meta_key,
 					'compare' => 'NOT EXISTS',
 				],
 			];
diff --git a/src/index.js b/src/index.js
index eecabf6..2a2623f 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,4 +1,4 @@
-/* global jQuery ajaxurl */
+/* global jQuery ajaxurl draggablePostOrder */
 
 import './index.scss';
 
@@ -35,6 +35,7 @@ import './index.scss';
 				ajaxurl,
 				{
 					action: 'update-post-order',
+					nonce: draggablePostOrder.nonce,
 					page: $( '#current-page-selector' ).val(),
 					perPage: $( '#edit_post_per_page' ).val(),
 					postOrder: $( '#the-list' ).sortable( 'serialize' ),
diff --git a/tests/test-adjacent-post-order.php b/tests/test-adjacent-post-order.php
new file mode 100644
index 0000000..80939cf
--- /dev/null
+++ b/tests/test-adjacent-post-order.php
@@ -0,0 +1,76 @@
+<?php
+/**
+ * Class TestAdjacentPostOrder
+ *
+ * @package DraggablePostOrder
+ */
+
+use Draggable_Post_Order\Draggable_Post_Order;
+
+/**
+ * Sample test case.
+ */
+class TestAdjacentPostOrder extends WP_UnitTestCase {
+
+	/**
+	 * An array of posts for testing.
+	 *
+	 * @var WP_Post[]
+	 */
+	public array $test_posts = [];
+
+	/**
+	 * Runs the routine before each test is executed.
+	 */
+	public function setUp(): void {
+		parent::setUp();
+
+		add_post_type_support( 'post', Draggable_Post_Order::$post_type_feature );
+
+		// create three posts with order.
+		for ( $i = 1; $i <= 3; $i++ ) {
+			$id = $this->factory()->post->create();
+			update_post_meta( $id, Draggable_Post_Order::$meta_key, $i );
+
+			$this->test_posts[] = get_post( $id );
+		}
+
+		// since tests are loaded after init, run init manually.
+		Draggable_Post_Order::init();
+	}
+
+	/**
+	 * Test previous and next post with creation order
+	 */
+	public function test_previous_next_post_creation_order() {
+		$first  = $this->test_posts[0];
+		$second = $this->test_posts[1];
+		$third  = $this->test_posts[2];
+
+		$this->go_to( '/?p=' . $second->ID );
+
+		$this->assertEquals( $first->ID, get_previous_post()->ID );
+		$this->assertEquals( $third->ID, get_next_post()->ID );
+	}
+
+	/**
+	 * Test previous and next post jumbled order
+	 */
+	public function test_previous_next_post_jumbled_order() {
+		$first  = $this->test_posts[1];
+		$second = $this->test_posts[2];
+		$third  = $this->test_posts[0];
+
+		update_post_meta( $first->ID, Draggable_Post_Order::$meta_key, 1 );
+		update_post_meta( $second->ID, Draggable_Post_Order::$meta_key, 2 );
+		update_post_meta( $third->ID, Draggable_Post_Order::$meta_key, 3 );
+
+		// test whether the key was set properly.
+		$this->assertEquals( 2, get_post_meta( $second->ID, Draggable_Post_Order::$meta_key, true ) );
+
+		$this->go_to( '/?p=' . $second->ID );
+
+		$this->assertEquals( $first->ID, get_previous_post()->ID );
+		$this->assertEquals( $third->ID, get_next_post()->ID );
+	}
+}
diff --git a/tests/test-post-order.php b/tests/test-post-order.php
index b5b26c7..7aa0be4 100644
--- a/tests/test-post-order.php
+++ b/tests/test-post-order.php
@@ -5,6 +5,8 @@
  * @package DraggablePostOrder
  */
 
+use Draggable_Post_Order\Draggable_Post_Order;
+
 /**
  * Sample test case.
  */
@@ -26,13 +28,13 @@ class TestPostOrder extends WP_UnitTestCase {
 		$this->test_post_type = register_post_type(
 			'test',
 			[
-				'supports'    => [ 'draggable-post-order' ],
+				'supports'    => [ Draggable_Post_Order::$post_type_feature ],
 				'has_archive' => true,
 			]
 		);
 
 		// since tests are loaded after init, run init manually.
-		\Draggable_Post_Order\Draggable_Post_Order::init();
+		Draggable_Post_Order::init();
 	}
 
 	/**
@@ -45,12 +47,12 @@ class TestPostOrder extends WP_UnitTestCase {
 		$meta_sub_query = [
 			'relation'                           => 'OR',
 			'draggable-post-order-clause'        => [
-				'key'  => 'draggable-post-order',
+				'key'  => Draggable_Post_Order::$meta_key,
 				'type' => 'NUMERIC',
 			],
 			// get all posts without the meta as well.
 			'draggable-post-order-exists-clause' => [
-				'key'     => 'draggable-post-order',
+				'key'     => Draggable_Post_Order::$meta_key,
 				'compare' => 'NOT EXISTS',
 			],
 		];