Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires infection/infection ^0.27.6 -> satisfiable by infection/infection[0.27.6]. - infection/infection 0.27.6 requires fidry/cpu-core-counter ^0.4.0 || ^0.5.0 -> found fidry/cpu-core-counter[0.4.0, 0.4.1, 0.5.0, 0.5.1] but it conflicts with your root composer.json require (^1.0.0).