Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires matthiasnoback/symfony-dependency-injection-test ^5.0 -> satisfiable by matthiasnoback/symfony-dependency-injection-test[5.0.0, 5.0.x-dev]. - matthiasnoback/symfony-dependency-injection-test[5.0.0, ..., 5.0.x-dev] require matthiasnoback/symfony-config-test ^5.0 -> found matthiasnoback/symfony-config-test[dev-master, v5.0.0, v5.1.0, 5.1.x-dev (alias of dev-master)] but it conflicts with your root composer.json require (^4.3).