Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires dms/phpunit-arraysubset-asserts dev-master -> satisfiable by dms/phpunit-arraysubset-asserts[dev-master]. - dms/phpunit-arraysubset-asserts dev-master requires phpunit/phpunit ^4.8.36 || ^5.7.21 || ^6.0 || ^7.0 || ^8.0 || ^9.0 || ^10.0 -> found phpunit/phpunit[4.8.36, 5.7.21, ..., 5.7.27, 6.0.0, ..., 6.5.14, 7.0.0, ..., 7.5.20, 8.0.0, ..., 8.5.42, 9.0.0, ..., 9.6.23, 10.0.0, ..., 10.5.48] but it conflicts with your root composer.json require (^12).