anchor.diff:    machine = { config, pkgs, ... }: (simpleConfig // {
         imports = [ ../modules/profiles/installation-device.nix
                     ../modules/profiles/base.nix ];
  -      virtualisation.memorySize = 1024;
  +      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;
  
positive.code: 
    testScript = ''
      # hack to add the secondary disk
      $machine->{startCommand} = "QEMU_OPTS=\"\$QEMU_OPTS \"${lib.escapeShellArg QEMU_OPTS} ".$machine->{startCommand};
  
      $machine->start;
      $machine->succeed("udevadm settle");
      $machine->waitForUnit("multi-user.target");
  
      # check that os-prober works standalone
      $machine->succeed("${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");
      $machine->copyFileFromHost(
          "${configFile}",
          "/etc/nixos/configuration.nix");
      $machine->succeed("nixos-rebuild boot >&2");
  
      $machine->succeed("egrep 'menuentry.*debian' /boot/grub/grub.cfg");
    '';
  })
  
negative.code:     '';
    };
  
    # a part of the configuration of the test vm
    simpleConfig = {
      boot.loader.grub = {
  