libxcrypt: add passthru tests

The shadow test uses a password that is hashed with libxcrypt and the
login test uses the passwd command.

pkgs/development/libraries/libxcrypt/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchurl, perl }:
+{ lib, stdenv, fetchurl, perl, nixosTests }:
 
 stdenv.mkDerivation rec {
   pname = "libxcrypt";
@@ -30,6 +30,10 @@ stdenv.mkDerivation rec {
 
   doCheck = !stdenv.hostPlatform.isMusl;
 
+  passthru.tests = {
+    inherit (nixosTests) login shadow;
+  };
+
   meta = with lib; {
     description = "Extended crypt library for descrypt, md5crypt, bcrypt, and others";
     homepage = "https://github.com/besser82/libxcrypt/";