Your requirements could not be resolved to an installable set of packages. Problem 1 - phpunit/phpunit[8.0.0, ..., 8.1.6] require sebastian/comparator ^3.0 -> found sebastian/comparator[3.0.0, ..., 3.0.5] but these were not loaded, likely because it conflicts with another require. - phpunit/phpunit[8.2.0, ..., 8.2.1] require phpspec/prophecy ^1.8.0 -> found phpspec/prophecy[1.8.0, ..., v1.18.0] but the package is fixed to v1.7.0 (lock file version) by a partial update and that version does not match. Make sure you list it as an argument for the update command. - phpunit/phpunit[8.2.2, ..., 8.5.8] require phpspec/prophecy ^1.8.1 -> found phpspec/prophecy[1.8.1, ..., v1.18.0] but the package is fixed to v1.7.0 (lock file version) by a partial update and that version does not match. Make sure you list it as an argument for the update command. - phpunit/phpunit[8.5.9, ..., 8.5.28] require phpspec/prophecy ^1.10.3 -> found phpspec/prophecy[v1.10.3, ..., v1.18.0] but the package is fixed to v1.7.0 (lock file version) by a partial update and that version does not match. Make sure you list it as an argument for the update command. - phpunit/phpunit 8.5.29 requires sebastian/comparator ^3.0.2 -> found sebastian/comparator[3.0.2, 3.0.3, 3.0.4, 3.0.5] but these were not loaded, likely because it conflicts with another require. - phpunit/phpunit[8.5.30, ..., 8.5.36] require sebastian/comparator ^3.0.5 -> found sebastian/comparator[3.0.5] but these were not loaded, likely because it conflicts with another require. - Root composer.json requires phpunit/phpunit ^8.0.0 -> satisfiable by phpunit/phpunit[8.0.0, ..., 8.5.36]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.