svoid test_uniqCI() {
  // try old & new mode
  for (bool collectForwardRefs : ll(true, false)) {
    new Concepts cc;
    cc.collectForwardRefs = collectForwardRefs;
    Concept a = cnew(cc, Concept);
    Concept b = uniqCI(cc, Concept, myRef := a);
    assertSameVerbose(cc, a.concepts());
    assertSameVerbose(cc, b.concepts());
    assertEqualsVerbose(a, cget(b, "myRef"));
    assertEqualsVerbose("refs field", collectForwardRefs, b._rawRefsField() != null);
    assertEqualsVerbose("num refs", 1, l(b._refs()));
    assertEqualsVerbose("num back refs", 1, l(a.backRefs));
    assertEquals(ll(b), findBackRefs(a));
  }
}