svoid test_DeepWordIndex() {
  new DeepWordIndex<S> index;
  index.add("a", "for (int i = 0; i < 5; i++) {}");
  index.add("b", "for (S x : y) {}");
  assertEqualsVerbose(ll(pair("a", ll(0))), asList(index.lookupString_withPositions("for (int i = 0", debug := true)));
  assertEqualsVerbose(ll(pair("a", ll(4))), asList(index.lookupString_withPositions("(int i = 0", debug := true)));
}