pppd: inherit nixos test into passthru.tests

pkgs/tools/networking/ppp/default.nix

···
 , libxcrypt
 , openssl
 , bash
+, nixosTests
 }:
 
 stdenv.mkDerivation rec {
···
   postFixup = ''
     substituteInPlace "$out/bin/pon" --replace "/usr/sbin" "$out/bin"
   '';
+
+  passthru.tests = {
+    inherit (nixosTests) pppd;
+  };
 
   meta = with lib; {
     homepage = "https://ppp.samba.org";