Fatal error: Uncaught Error: Class 'Composer\Installer\LibraryInstaller' not found in E:\xampp\htdocs\www\TT\ThinkPHP\vendor\topthink\think-installer\src\ThinkTesting.php:19 Stack trace: #0 {main} thrown in E:\xampp\htdocs\www\TT\ThinkPHP\vendor\topthink\think-installer\src\ThinkTesting.php on line 19