diff --git a/tests/phpunit/tests/admin/includes/ajax-actions/addMenuItem.php b/tests/phpunit/tests/admin/includes/ajax-actions/addMenuItem.php
new file mode 100644
index 0000000000000..2a4cd67f476e8
--- /dev/null
+++ b/tests/phpunit/tests/admin/includes/ajax-actions/addMenuItem.php
@@ -0,0 +1,174 @@
+<?php
+
+/**
+ * Admin Ajax functions to be tested.
+ */
+require_once ABSPATH . 'wp-admin/includes/ajax-actions.php';
+
+/**
+ * Testing wp_ajax_add_menu_item() functionality.
+ *
+ * @package WordPress
+ * @subpackage UnitTests
+ * @since 3.1.0
+ *
+ * @group ajax
+ *
+ * @covers ::wp_ajax_add_menu_item
+ */
+class Tests_wp_ajax_add_menu_item extends WP_Ajax_UnitTestCase {
+
+	/**
+	 * Administrator user ID.
+	 *
+	 * @var int
+	 */
+	protected static $admin_id;
+
+	/**
+	 * Subscriber user ID.
+	 *
+	 * @var int
+	 */
+	protected static $subscriber_id;
+
+	/**
+	 * Setup test fixtures.
+	 *
+	 * @param WP_UnitTest_Factory $factory
+	 */
+	public static function wpSetUpBeforeClass( WP_UnitTest_Factory $factory ): void {
+		self::$admin_id      = $factory->user->create( array( 'role' => 'administrator' ) );
+		self::$subscriber_id = $factory->user->create( array( 'role' => 'subscriber' ) );
+	}
+
+	/**
+	 * Setup before each test method.
+	 */
+	public function set_up(): void {
+		parent::set_up();
+		add_action( 'admin_init', array( $this, 'hook_ajax_handler' ), 1 );
+	}
+
+	/**
+	 * Hooks the AJAX handler to admin_init.
+	 */
+	public function hook_ajax_handler(): void {
+		if ( isset( $_POST['action'] ) && 'add-menu-item' === $_POST['action'] ) {
+			wp_ajax_add_menu_item();
+		}
+	}
+
+	/**
+	 * Tests successful addition of a custom menu item.
+	 *
+	 * @ticket 65252
+	 */
+	public function test_add_menu_item_custom_success(): void {
+		wp_set_current_user( self::$admin_id );
+
+		$_POST = array(
+			'action'                     => 'add-menu-item',
+			'menu-settings-column-nonce' => wp_create_nonce( 'add-menu_item' ),
+			'menu-item'                  => array(
+				array(
+					'menu-item-type'  => 'custom',
+					'menu-item-title' => 'Custom Link',
+					'menu-item-url'   => 'https://example.com',
+				),
+			),
+		);
+
+		try {
+			$this->_handleAjax( 'add-menu-item' );
+		} catch ( WPAjaxDieStopException $e ) {
+			$response = $e->getMessage();
+			$this->assertStringContainsString( 'Custom Link', $response );
+			$this->assertStringContainsString( 'https://example.com', $response );
+		} catch ( WPAjaxDieContinueException $e ) {
+			$response = $this->_last_response;
+			$this->assertStringContainsString( 'Custom Link', $response );
+			$this->assertStringContainsString( 'https://example.com', $response );
+		}
+	}
+
+	/**
+	 * Tests successful addition of a post menu item.
+	 *
+	 * @ticket 65252
+	 */
+	public function test_add_menu_item_post_success(): void {
+		$factory = self::factory();
+		wp_set_current_user( self::$admin_id );
+
+		$post_id = $factory->post->create(
+			array(
+				'post_title' => 'Test Page',
+				'post_type'  => 'page',
+			)
+		);
+
+		$_POST = array(
+			'action'                      => 'add-menu-item',
+			'menu-settings-column-nonce'  => wp_create_nonce( 'add-menu_item' ),
+			'menu-item'                   => array(
+				array(
+					'menu-item-type'      => 'post_type',
+					'menu-item-object'    => 'page',
+					'menu-item-object-id' => $post_id,
+				),
+			),
+		);
+
+		try {
+			$this->_handleAjax( 'add-menu-item' );
+		} catch ( WPAjaxDieStopException $e ) {
+			$response = $e->getMessage();
+			$this->assertStringContainsString( 'Test Page', $response );
+		} catch ( WPAjaxDieContinueException $e ) {
+			$response = $this->_last_response;
+			$this->assertStringContainsString( 'Test Page', $response );
+		}
+	}
+
+	/**
+	 * Tests addition failure due to invalid nonce.
+	 *
+	 * @ticket 65252
+	 */
+	public function test_add_menu_item_invalid_nonce(): void {
+		wp_set_current_user( self::$admin_id );
+
+		$_POST = array(
+			'action'                      => 'add-menu-item',
+			'menu-settings-column-nonce'  => 'invalid-nonce',
+		);
+
+		$this->expectException( WPAjaxDieStopException::class );
+		$this->expectExceptionMessage( '-1' );
+
+		$this->_handleAjax( 'add-menu-item' );
+	}
+
+	/**
+	 * Tests addition failure due to insufficient permissions.
+	 *
+	 * @ticket 65252
+	 */
+	public function test_add_menu_item_insufficient_permissions(): void {
+		wp_set_current_user( self::$subscriber_id );
+
+		$_POST = array(
+			'action'                      => 'add-menu-item',
+			'menu-settings-column-nonce'  => wp_create_nonce( 'add-menu_item' ),
+		);
+
+		try {
+			$this->_handleAjax( 'add-menu-item' );
+		} catch ( WPAjaxDieStopException $e ) {
+			$this->assertSame( '-1', $e->getMessage() );
+		} catch ( WPAjaxDieContinueException $e ) {
+			$this->assertSame( '-1', $e->getMessage() );
+		}
+	}
+}