Since c37e76b machinectl shell is used to run commands inside containers instead of nsenter + su. However machinectl shell does not forward the return code of the command to the caller (see systemd/systemd#4215) so all the tests that use nixos-container run always succeed (e.g container-physical_interfaces.nix). So as long as systemd/systemd#4215 is not solved some tests may succeed when in fact they should have failed.