nixos/systemd-boot: add test for devicetree

      imports = [ common ];

      specialisation.something.configuration = {

        boot.loader.systemd-boot.sortKey = "something";

        # Since qemu will dynamically create a devicetree blob when starting

        # up, it is not straight forward to create an export of that devicetree

        # blob without knowing before-hand all the flags we would pass to qemu

        # (we would then be able to use `dumpdtb`). Thus, the following config

        # will not boot, but it does allow us to assert that the boot entry has

        # the correct contents.

        boot.loader.systemd-boot.installDeviceTree = pkgs.stdenv.hostPlatform.isAarch64;

        hardware.deviceTree.name = "dummy.dtb";

        hardware.deviceTree.package = lib.mkForce (pkgs.runCommand "dummy-devicetree-package" { } ''

          mkdir -p $out

          cp ${pkgs.emptyFile} $out/dummy.dtb

        '');

      };

    };

    testScript = ''

    testScript = { nodes, ... }: ''

      machine.start()

      machine.wait_for_unit("multi-user.target")

      machine.succeed(

          "grep 'sort-key something' /boot/loader/entries/nixos-generation-1-specialisation-something.conf"

      )

    '' + pkgs.lib.optionalString pkgs.stdenv.hostPlatform.isAarch64 ''

      machine.succeed(

          "grep 'devicetree .*dummy' /boot/loader/entries/nixos-generation-1-specialisation-something.conf"

      )

    '';

  };