anchor.diff:        $client->succeed("chmod 600 /root/.ssh/id_dsa");
   
         # Install the SSH key on the slaves.
  -      $slave1->succeed("mkdir -m 700 /root/.ssh");
  -      $slave1->copyFileFromHost("key.pub", "/root/.ssh/authorized_keys");
  -      $slave1->waitForJob("sshd");
  -      $client->succeed("ssh -o StrictHostKeyChecking=no slave1 'echo hello world'");
  +      foreach my $slave ($slave1, $slave2) {
  +          $slave->succeed("mkdir -m 700 /root/.ssh");
  +          $slave->copyFileFromHost("key.pub", "/root/.ssh/authorized_keys");
  +          $slave->waitForJob("sshd");
  +          $client->succeed("ssh -o StrictHostKeyChecking=no " . $slave->name() . " 'echo hello world'");
  +      }
   
         # Perform a build and check that it was performed on the slave.
  -      my $out = $client->succeed("nix-build ${expr nodes.client.config}");
  +      my $out = $client->succeed("nix-build ${expr nodes.client.config 1}");
         $slave1->succeed("test -e $out");
  +
  +      # And a parallel build.
  +      my ($out1, $out2) = split /\s/,
  +          $client->succeed("nix-store -r \$(nix-instantiate ${expr nodes.client.config 2} ${expr nodes.client.config 3})");
  +      $slave1->succeed("test -e $out1 -o -e $out2");
  +      $slave2->succeed("test -e $out1 -o -e $out2");
       '';
   
   }
  
positive.code:     };
  
    # Trivial Nix expression to build remotely.
    expr = config: pkgs.writeText "expr.nix"
      ''
        let utils = builtins.storePath ${config.system.build.extraUtils}; in
        derivation {
          name = "hello";
          system = "i686-linux";
          PATH = "''${utils}/bin";
          builder = "''${utils}/bin/sh";
          args = [ "-c" "echo Hello; mkdir $out; cat /proc/sys/kernel/hostname > $out/host" ];
        }
      '';
  
  
negative.code: 
    nodes =
      { slave1 = slave;
        slave2 = slave;
  
        client =
          { config, pkgs, ... }:
  