Iterable<T> unmodifiable, Iterable<T> modifiable) {
    UnmodifiableCollectionTests.assertIteratorIsUnmodifiable(unmodifiable.iterator());
    UnmodifiableCollectionTests.assertIteratorsInOrder(
        unmodifiable.iterator(), modifiable.iterator());
  }

  public void testInvertFrom() {
    ImmutableMultimap<Integer, String> empty = ImmutableMultimap.of();