{
  config = {
    programs.ssh = {
      enable = true;
      enableDefaultConfig = false;
      settings = {
        remoteHostPathWithPort = {
          RemoteForward = [
            {
              # OK:
              bind.address = "127.0.0.1";
              bind.port = 3000;

              # Error:
              host.address = "/run/user/1000/gnupg/S.gpg-agent.extra";
              host.port = 3000;
            }
          ];
        };
      };
    };

    test.asserts.assertions.expected = [ "Forwarded paths cannot have ports." ];
  };
}
