scope test_unstructureMissingConcept.

concept Blu { Blu ref; }

svoid test_unstructureMissingConcept() {
  Blu b = unlisted(Blu);
  b.ref = b;
  new structure_Data data;
  data.storeBaseClasses = true; // try with this new feature
  S struct = structure(b, data);
  print(+struct);
  O o = unstructure(struct, true);
  assertEqualsVerbose(Concept.class, _getClass(o));
  assertSameVerbose(o, cget(o, "ref"));
}

end scope

Began life as a copy of #1030942