Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires simpletest/simpletest ^1.3, it is satisfiable by simpletest/simpletest[v1.3.0] from composer repo (https://repo.packagist.org) but simpletest/simpletest[dev-master, 1.1.3, ..., v1.1.7] from vcs repo (github https://github.com/ezyang/simpletest.git) has higher repository priority. The packages from the higher priority repository do not match your constraint and are therefore not installable. That repository is canonical so the lower priority repo's packages are not installable. See https://getcomposer.org/repoprio for details and assistance.