strongswan: add strongswan-swanctl test to passthru.tests

pkgs/tools/networking/strongswan/default.nix

@@ -7,6 +7,7 @@
 , enableTNC            ? false, trousers, sqlite, libxml2
 , enableNetworkManager ? false, networkmanager
 , darwin
+, nixosTests
 }:
 
 # Note on curl support: If curl is built with gnutls as its backend, the
@@ -101,6 +102,8 @@ stdenv.mkDerivation rec {
 
   NIX_LDFLAGS = optionalString stdenv.cc.isGNU "-lgcc_s" ;
 
+  passthru.tests = { inherit (nixosTests) strongswan-swanctl; };
+
   meta = {
     description = "OpenSource IPsec-based VPN Solution";
     homepage = "https://www.strongswan.org";