anchor.diff:              Type = "oneshot";
               ExecStart = "${pkgs.writeScriptBin "test-script" ''
                 #!${bash}/bin/bash
  -              "${cfg.test-driver.script}" >> stdout 2>> stderr || touch failed
  +              "${cfg.test-driver.script}" >> log/stdout 2>> log/stderr || touch failed
                 sync -f .
                 ${pkgs.systemd}/bin/systemctl poweroff --force
               ''}/bin/test-script";
  
positive.code:       tailFiles = mkOption {
          type = with types; attrsOf str;
          default = {
            OUT = "stdout";
            ERR = "stderr";
          } // genAttrs instNames (n: "hosts/${n}/console.log")
            // genAttrs instNames (n: "hosts/${n}/journal.log");
        };
  
        test-driver = {
  
negative.code:         mkdir -p $out/nix-support
  
          (
            echo "file log $out/log/stdout"
            echo "file log $out/log/stderr"
            for i in ${toString instNames}; do for l in console journal; do
              echo "file log $out/log/$i-$l.log"
            done; done
          ) >> $out/nix-support/hydra-build-products
  
  