diff --git a/tests/phpunit/tests/admin/includes/ajax-actions/widgetsOrder.php b/tests/phpunit/tests/admin/includes/ajax-actions/widgetsOrder.php
new file mode 100644
index 0000000000000..c54759b078e73
--- /dev/null
+++ b/tests/phpunit/tests/admin/includes/ajax-actions/widgetsOrder.php
@@ -0,0 +1,128 @@
+<?php
+
+/**
+ * Admin Ajax functions to be tested.
+ */
+require_once ABSPATH . 'wp-admin/includes/ajax-actions.php';
+
+/**
+ * Testing wp_ajax_widgets_order() functionality.
+ *
+ * @package WordPress
+ * @subpackage UnitTests
+ * @since 3.1.0
+ *
+ * @group ajax
+ *
+ * @covers ::wp_ajax_widgets_order
+ */
+class Tests_wp_ajax_widgets_order extends WP_Ajax_UnitTestCase {
+
+	/**
+	 * Administrator user ID.
+	 *
+	 * @var int
+	 */
+	protected static $admin_id;
+
+	/**
+	 * Setup test fixtures.
+	 *
+	 * @param WP_UnitTest_Factory $factory
+	 */
+	public static function wpSetUpBeforeClass( WP_UnitTest_Factory $factory ): void {
+		self::$admin_id = $factory->user->create( array( 'role' => 'administrator' ) );
+	}
+
+	/**
+	 * Tests successful widgets order saving.
+	 *
+	 * @ticket 65252
+	 */
+	public function test_widgets_order_success(): void {
+		wp_set_current_user( self::$admin_id );
+
+		// Mock sidebars.
+		$sidebars = array(
+			'sidebar-1' => 'widget-1_text-1,widget-2_text-2',
+			'sidebar-2' => 'widget-3_search-1',
+		);
+
+		$_POST = array(
+			'action'      => 'widgets-order',
+			'savewidgets' => wp_create_nonce( 'save-sidebar-widgets' ),
+			'sidebars'    => $sidebars,
+		);
+
+		try {
+			$this->_handleAjax( 'widgets-order' );
+		} catch ( WPAjaxDieContinueException $e ) {
+			// Expect success.
+		}
+
+		$this->assertSame( '1', $this->_last_response );
+
+		$updated_sidebars = wp_get_sidebars_widgets();
+		$this->assertContains( 'text-1', $updated_sidebars['sidebar-1'] );
+		$this->assertContains( 'text-2', $updated_sidebars['sidebar-1'] );
+		$this->assertContains( 'search-1', $updated_sidebars['sidebar-2'] );
+	}
+
+	/**
+	 * Tests failure due to invalid nonce.
+	 *
+	 * @ticket 65252
+	 */
+	public function test_widgets_order_invalid_nonce(): void {
+		wp_set_current_user( self::$admin_id );
+
+		$_POST = array(
+			'action'      => 'widgets-order',
+			'savewidgets' => 'invalid-nonce',
+		);
+
+		$this->expectException( WPAjaxDieStopException::class );
+		$this->expectExceptionMessage( '-1' );
+
+		$this->_handleAjax( 'widgets-order' );
+	}
+
+	/**
+	 * Tests failure due to insufficient permissions.
+	 *
+	 * @ticket 65252
+	 */
+	public function test_widgets_order_insufficient_permissions(): void {
+		$user_id = self::factory()->user->create( array( 'role' => 'subscriber' ) );
+		wp_set_current_user( $user_id );
+
+		$_POST = array(
+			'action'      => 'widgets-order',
+			'savewidgets' => wp_create_nonce( 'save-sidebar-widgets' ),
+		);
+
+		$this->expectException( WPAjaxDieStopException::class );
+		$this->expectExceptionMessage( '-1' );
+
+		$this->_handleAjax( 'widgets-order' );
+	}
+
+	/**
+	 * Tests behavior when sidebars parameter is missing.
+	 *
+	 * @ticket 65252
+	 */
+	public function test_widgets_order_missing_sidebars(): void {
+		wp_set_current_user( self::$admin_id );
+
+		$_POST = array(
+			'action'      => 'widgets-order',
+			'savewidgets' => wp_create_nonce( 'save-sidebar-widgets' ),
+		);
+
+		$this->expectException( WPAjaxDieStopException::class );
+		$this->expectExceptionMessage( '-1' );
+
+		$this->_handleAjax( 'widgets-order' );
+	}
+}