lowdown: add nix to passthru.tests

pkgs/tools/typesetting/lowdown/default.nix

@@ -1,6 +1,8 @@
 { lib, stdenv, fetchurl, fixDarwinDylibNames, which
 , enableShared ? !(stdenv.hostPlatform.isStatic)
 , enableStatic ? stdenv.hostPlatform.isStatic
+# for passthru.tests
+, nix
 }:
 
 stdenv.mkDerivation rec {
@@ -69,6 +71,11 @@ stdenv.mkDerivation rec {
   doCheck = true;
   checkTarget = "regress";
 
+  passthru.tests = {
+    # most important consumer in nixpkgs
+    inherit nix;
+  };
+
   meta = with lib; {
     homepage = "https://kristaps.bsd.lv/lowdown/";
     description = "Simple markdown translator";