Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit 8.5.38 -> satisfiable by phpunit/phpunit[8.5.38]. - phpunit/phpunit 8.5.38 requires php >=7.2 -> your php version (7.1.33) does not satisfy that requirement. Problem 2 - phpunit/phpunit 8.5.38 requires php >=7.2 -> your php version (7.1.33) does not satisfy that requirement. - yoast/phpunit-polyfills 2.0.0 requires phpunit/phpunit ^5.7.21 || ^6.0 || ^7.0 || ^8.0 || ^9.0 || ^10.0 -> satisfiable by phpunit/phpunit[8.5.38]. - Root composer.json requires yoast/phpunit-polyfills 2.0.0 -> satisfiable by yoast/phpunit-polyfills[2.0.0].