saunafs: add VM test to passthru.test

pkgs/by-name/sa/saunafs/package.nix

@@ -1,6 +1,7 @@
 {
   lib,
   stdenv,
+  nixosTests,
   fetchFromGitHub,
   cmake,
   asciidoc,
@@ -64,6 +65,8 @@ stdenv.mkDerivation (finalAttrs: {
     ln -s $out/bin/sfsmount $out/bin/mount.saunafs
   '';
 
+  passthru.tests = nixosTests.saunafs;
+
   meta = with lib; {
     description = "Distributed POSIX file system";
     homepage = "https://saunafs.com";