svoid test_metaTransformer_transformableAndList() {
  transformable record Rec(S yo) {}
  
  IF1 f = o -> o instanceof S ? upper(o/S) : null;
  MetaTransformer tf = metaTransformer_transformableAndList();
  
  assertEqualsVerbose(ll("BLA", "BLU"), tf.transform(f, ll("bla", "blu")));
  assertEqualsVerbose(ll(new Rec("TEST"), 5), tf.transform(f, ll(new Rec("test"), 5)));
}