Add tests for console commands #473
Description
In #467 I broke the application because I made a wrong choice and we don't have tests for console commands.
I'm not sure if we need tests for ALL commands. Maybe we can just test app:add-user because it's complex enough. Let's use the new setInputs() feature to tests commands. See https://symfony.com/doc/current/components/console/helpers/questionhelper.html#testing-a-command-that-expects-input