Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit ^12.0.0 -> satisfiable by phpunit/phpunit[12.0.0, 12.0.1]. - phpunit/phpunit[12.0.0, ..., 12.0.1] require php >=8.3 -> your php version (8.1.31) does not satisfy that requirement. Problem 2 - Root composer.json requires php-mock/php-mock-phpunit ^2.8.0 -> satisfiable by php-mock/php-mock-phpunit[2.8.0, 2.9.0, 2.10.0]. - php-mock/php-mock-phpunit 2.10.0 requires phpunit/phpunit ^6 || ^7 || ^8 || ^9 || ^10.0.17 || ^11 -> found phpunit/phpunit[6.0.0, ..., 6.5.14, 7.0.0, ..., 7.5.20, 8.0.0, ..., 8.5.41, 9.0.0, ..., 9.6.22, 10.0.17, ..., 10.5.45, 11.0.0, ..., 11.5.7] but it conflicts with your root composer.json require (^12.0.0). - php-mock/php-mock-phpunit[2.8.0, ..., 2.9.0] require phpunit/phpunit ^6 || ^7 || ^8 || ^9 || ^10.0.17 -> found phpunit/phpunit[6.0.0, ..., 6.5.14, 7.0.0, ..., 7.5.20, 8.0.0, ..., 8.5.41, 9.0.0, ..., 9.6.22, 10.0.17, ..., 10.5.45] but it conflicts with your root composer.json require (^12.0.0). Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.