lib:
let
  overrideExistingOld =
    old:
    new:
    builtins.mapAttrs (name: value: new.${name} or value) old;

  overrideExistingNew =
    old:
    new:
    old // (builtins.intersectAttrs old new);

  bigdata = lib.genAttrs (lib.imap0 (i: _: toString i) (lib.replicate 999999 null)) (_: null);
  attrsToOverride = {
    "1" = "lmao";
    "183" = "lmao";
    "1823" = "lmao";
    "1223" = "lmao";
    "ads;fkjasdlfkja" = "no";
  };
in {
  old = overrideExistingOld bigdata attrsToOverride;
  new = overrideExistingNew bigdata attrsToOverride;
  sanity = (overrideExistingOld bigdata attrsToOverride) == (overrideExistingNew bigdata attrsToOverride);
}