hercules-ci-agent: Improve passthru tests

    };

    passthru = o.passthru // {

      # Does not test the package, but evaluation of the related NixOS module.

      tests.nixos-minimal-config = nixos {

      tests.nixos-simple-config = (nixos {

        boot.loader.grub.enable = false;

        fileSystems."/".device = "bogus";

        services.hercules-ci-agent.enable = true;

        # Dummy value for testing only.

        system.stateVersion = lib.trivial.release; # TEST ONLY

      }).config.system.build.toplevel;

      tests.nixos-many-options-config = (nixos ({ pkgs, ... }: {

        boot.loader.grub.enable = false;

        fileSystems."/".device = "bogus";

        services.hercules-ci-agent = {

          enable = true;

          package = pkgs.hercules-ci-agent;

          settings = {

            workDirectory = "/var/tmp/hci";

            binaryCachesPath = "/var/keys/binary-caches.json";

            labels.foo.bar.baz = "qux";

            labels.qux = ["q" "u"];

            apiBaseUrl = "https://hci.dev.biz.example.com";

            concurrentTasks = 42;

          };

        };

        # Dummy value for testing only.

        system.stateVersion = lib.trivial.release; # TEST ONLY

      })).config.system.build.toplevel;

    };

  })