anchor.diff:  
   
     buildVM =
  -    nodes: configuration:
  +    nodes: configurations:
   
       import "${nixos}/lib/eval-config.nix" {
         inherit nixpkgs services system;
  -      modules = [ configuration ];
  +      modules = configurations ++ [
  +        "${nixos}/modules/virtualisation/qemu-vm.nix" # !!!
  +        "${nixos}/modules/testing/test-instrumentation.nix" # !!! should only get added for automated test runs
  +      ];
         extraArgs = { inherit nodes; };
         /* !!! bug in the module/option handling: this ignores the
            config from assignIPAddresses.  Too much magic. 
  
positive.code:       # Generate a /etc/hosts file.
        hosts = lib.concatMapStrings (m: "${m.second} ${m.first}\n") machinesWithIP;
  
        nodes_ = map (m: lib.nameValuePair m.first
            { imports = [
                (lib.getAttr m.first nodes)
                "${nixos}/modules/virtualisation/qemu-vm.nix" # !!!
                "${nixos}/modules/testing/test-instrumentation.nix" # !!! should only get added for automated test runs
              ];
              config =
                { networking.hostName = m.first;
                  networking.interfaces =
                    [ { name = "eth1";
  
negative.code:                 services.nixosManual.enable = false; # !!!
                };
            }
            (lib.getAttr m.first nodes)
          ]) machinesWithIP;
  
      in lib.listToAttrs nodes_;
  
  