anchor.diff:        $machine = createMachine({ ${hdFlags} qemuFlags => "${qemuFlags}" });
         $machine->waitForUnit("multi-user.target");
         $machine->copyFileFromHost(
  -          "${ makeConfig { inherit testChannel grubVersion grubDevice grubIdentifier; readOnly = false; forceGrubReinstallCount = 2; } }",
  +          "${ makeConfig { inherit testChannel grubVersion grubDevice grubIdentifier extraConfig; readOnly = false; forceGrubReinstallCount = 2; } }",
             "/etc/nixos/configuration.nix");
         $machine->succeed("nixos-rebuild boot >&2");
         $machine->shutdown;
  
positive.code:       $machine->succeed("cat /mnt/etc/nixos/hardware-configuration.nix >&2");
  
        $machine->copyFileFromHost(
            "${ makeConfig { inherit testChannel grubVersion grubDevice grubIdentifier; } }",
            "/mnt/etc/nixos/configuration.nix");
  
        # Perform the installation.
  
negative.code: 
  
    makeInstallerTest = name:
      { createPartitions, testChannel ? false, grubVersion ? 2
      , grubDevice ? "/dev/vda", grubIdentifier ? "uuid", extraConfig ? ""
      }:
      makeTest {
        inherit iso;
        name = "installer-" + name;
        nodes = if testChannel then { inherit webserver; } else { };
        testScript = testScriptFun {
          inherit createPartitions testChannel grubVersion grubDevice
                  grubIdentifier extraConfig;
        };
      };
  
  