Your requirements could not be resolved to an installable set of packages.
Problem 1
- silverstripe/recipe-testing[2.0.0, ..., 2.x-dev] require silverstripe/framework ^4.10 -> found silverstripe/framework[4.10.0-beta1, ..., 4.x-dev] but it conflicts with your root composer.json require (^5.0).
- Root composer.json requires silverstripe/recipe-testing ^2 -> satisfiable by silverstripe/recipe-testing[2.0.0, 2.0.x-dev, 2.x-dev].