varnish: add passthru.tests

pkgs/servers/varnish/default.nix

@@ -1,5 +1,5 @@
 { lib, stdenv, fetchurl, fetchpatch, pcre, pcre2, jemalloc, libxslt, groff, ncurses, pkg-config, readline, libedit
-, coreutils, python3, makeWrapper }:
+, coreutils, python3, makeWrapper, nixosTests }:
 
 let
   common = { version, hash, extraNativeBuildInputs ? [] }:
@@ -12,8 +12,6 @@ let
         inherit hash;
       };
 
-      passthru.python = python3;
-
       nativeBuildInputs = with python3.pkgs; [ pkg-config docutils sphinx makeWrapper];
       buildInputs = [
         libxslt groff ncurses readline libedit python3
@@ -37,6 +35,11 @@ let
 
       outputs = [ "out" "dev" "man" ];
 
+      passthru = {
+        python = python3;
+        tests = nixosTests."varnish${builtins.replaceStrings [ "." ] [ "" ] (lib.versions.majorMinor version)}";
+      };
+
       meta = with lib; {
         broken = stdenv.isDarwin;
         description = "Web application accelerator also known as a caching HTTP reverse proxy";