Plugin to simulate plugin/theme update failure for testing Rollback Update Failure feature plugin.

rollback-testing.php

<?php
/**
 * Rollback Update Testing
 *
 * @package rollback-update-testing
 * @author Andy Fragen <andy@thefragens.com>
 * @license MIT
 */

/**
 * Plugin Name:       Rollback Update Testing
 * Plugin URI:        https://gist.github.com/afragen/80b68a6c8826ab37025b05d4519bb4bf
 * Description:       This plugin is used for Rollback Update Failure feature plugin testing to randomly simulate an update failure.
 * Version:           0.5.0
 * Author:            WordPress Core Contributors
 * License:           MIT
 * Requires at least: 5.2
 * Requires PHP:      5.6
 * Gist Plugin URI:   https://gist.github.com/afragen/80b68a6c8826ab37025b05d4519bb4bf
 */

//add_filter(
	//'upgrader_install_package_result',
	//function() {
		// return new WP_Error( 'simulated_error', 'Simulated Error' );
	//}
//);

add_filter(
	'upgrader_install_package_result',
	function( $result, $hook_extra ) {
		// update-core.php selected.
		$plugins_selected = isset( $_GET['plugins'] ) ? explode( ',', $_GET['plugins'] ) : [];

		// plugins.php selected.
		$plugins_selected = isset( $_POST['plugin'] ) ? explode( ',', $_POST['plugin'] ) : $plugins_selected;

		$plugin_to_fail = $plugins_selected;
		unset( $plugin_to_fail[ random_int( 0, count( $plugins_selected ) - 1 ) ] );

		if ( isset( $hook_extra['plugin'] ) && in_array( $hook_extra['plugin'], $plugin_to_fail, true ) ) {
			return new WP_Error( 'simulated_error', 'Simulated Error' );
		}

		return $result;
	},
	10,
	2
);