nixos/tests: add snapcast

Checks
- if all configured ports are listened on
- if all pipes for multiple streams get set up
- if rpc interaction is possible

pkgs/applications/audio/snapcast/default.nix

@@ -1,5 +1,6 @@
 { stdenv, lib, fetchFromGitHub, cmake, pkgconfig
-, alsaLib, asio, avahi, boost170, flac, libogg, libvorbis, soxr }:
+, alsaLib, asio, avahi, boost170, flac, libogg, libvorbis, soxr
+, nixosTests }:
 
 let
 
@@ -57,6 +58,8 @@ stdenv.mkDerivation rec {
     cp -r ../doc/* ../*.md $out/share/doc/snapcast
   '';
 
+  passthru.tests.snapcast = nixosTests.snapcast;
+
   meta = with lib; {
     description = "Synchronous multi-room audio player";
     homepage = "https://github.com/badaix/snapcast";