svoid test_deepDoubleWordIndex_lookupString() {
  new DoubleWordIndex<WithIntArray<S>> index;
  deepDoubleWordIndex_add(index, "a", "hello world");
  assertEqualsVerbose(ll("a"), asList(deepDoubleWordIndex_lookupString(index, "hello")));
  assertEqualsVerbose(ll("a"), asList(deepDoubleWordIndex_lookupString(index, "hello world", debug := true)));
}