anchor.diff:  
     testScript = ''
       # hack to add the secondary disk
  -    $machine->{startCommand} = "QEMU_OPTS=\"\$QEMU_OPTS \"${lib.escapeShellArg QEMU_OPTS} ".$machine->{startCommand};
  +    os.environ[
  +        "QEMU_OPTS"
  +    ] = "-drive index=2,file=${debianImage}/disk-image.qcow2,read-only,if=virtio"
   
  -    $machine->start;
  -    $machine->succeed("udevadm settle");
  -    $machine->waitForUnit("multi-user.target");
  +    machine.start()
  +    machine.succeed("udevadm settle")
  +    machine.wait_for_unit("multi-user.target")
  +    print(machine.succeed("lsblk"))
   
       # check that os-prober works standalone
  -    $machine->succeed("${pkgs.os-prober}/bin/os-prober | grep /dev/vdb1");
  +    machine.succeed(
  +        "${pkgs.os-prober}/bin/os-prober | grep /dev/vdb1"
  +    )
   
       # rebuild and test that debian is available in the grub menu
  -    $machine->succeed("nixos-generate-config");
  -    $machine->copyFileFromHost(
  +    machine.succeed("nixos-generate-config")
  +    machine.copy_from_host(
           "${configFile}",
  -        "/etc/nixos/configuration.nix");
  -    $machine->succeed("nixos-rebuild boot >&2");
  +        "/etc/nixos/configuration.nix",
  +    )
  +    machine.succeed("nixos-rebuild boot >&2")
   
  -    $machine->succeed("egrep 'menuentry.*debian' /boot/grub/grub.cfg");
  +    machine.succeed("egrep 'menuentry.*debian' /boot/grub/grub.cfg")
     '';
   })
  
positive.code:     '';
    };
  
    # options to add the disk to the test vm
    QEMU_OPTS = "-drive index=2,file=${debianImage}/disk-image.qcow2,read-only,if=virtio";
  
    # a part of the configuration of the test vm
    simpleConfig = {
      boot.loader.grub = {
  
negative.code:   machine = { config, pkgs, ... }: (simpleConfig // {
        imports = [ ../modules/profiles/installation-device.nix
                    ../modules/profiles/base.nix ];
        virtualisation.memorySize = 1300;
        # The test cannot access the network, so any packages
        # nixos-rebuild needs must be included in the VM.
        system.extraDependencies = with pkgs;
  