flake.nix

{
  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-20.03";
  inputs.nixpkgs-unstable.url = "github:NixOS/nixpkgs/nixos-unstable";
  inputs.hydra.url = "github:NixOS/hydra";
  
  outputs = { self, nixpkgs, nixpkgs-unstable, hydra }: {

    nixosConfigurations.container = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules =
        [ ./test.nix # tries to reference stuff in `hydra` from above
          ({ pkgs, ... }: {
            boot.isContainer = true;

            # Let 'nixos-version --json' know about the Git revision
            # of this flake.
            system.configurationRevision = nixpkgs-unstable.lib.mkIf (self ? rev) self.rev;

            # Network configuration.
            networking.useDHCP = false;
            networking.firewall.allowedTCPPorts = [ 80 ];

            # Enable a web server.
            services.httpd = {
              enable = true;
              adminAddr = "morty@example.org";
            };
          })
        ];
    };

  };
}

test.nix

{ hydra, ... }: {
  require =[ hydra.nixosModules.hydraTest ];
}