cups: Add passthru printing test

pkgs/misc/cups/default.nix

@@ -18,11 +18,9 @@
 , avahi ? null
 , libpaper ? null
 , coreutils
+, nixosTests
 }:
 
-### IMPORTANT: before updating cups, make sure the nixos/tests/printing.nix test
-### works at least for your platform.
-
 with lib;
 stdenv.mkDerivation rec {
   pname = "cups";
@@ -137,6 +135,8 @@ stdenv.mkDerivation rec {
         --replace "Exec=htmlview" "Exec=xdg-open"
     '';
 
+  passthru.tests.nixos = nixosTests.printing;
+
   meta = {
     homepage = "https://openprinting.github.io/cups/";
     description = "A standards-based printing system for UNIX";