Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires infection/infection ^0.27.11 -> satisfiable by infection/infection[0.27.11, 0.27.x-dev]. - infection/infection[0.27.11, ..., 0.27.x-dev] require nikic/php-parser ^4.15.1 -> found nikic/php-parser[v4.15.1, ..., 4.x-dev] but it conflicts with your root composer.json require (^5.4.0). Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.