svoid test_WordIndex() {
  new WordIndex<S> idx;
  idx.add("hello world");
  idx.add("yo WOrLD");
  assertEqualsVerbose(ll("hello world"), idx.get("hello"));
  assertEqualsVerbose(ll("hello world", "yo WOrLD"), idx.get("world"));
  assertEqualsVerbose(ll(), idx.get("something else"));
  idx.remove("yo WOrLD");
  assertEqualsVerbose(ll("hello world"), idx.get("hello"));
  assertEqualsVerbose(ll("hello world"), idx.get("world"));
  assertEqualsVerbose(ll(), idx.get("something else"));
}