@Test public void testFlatteningToImmutableSetMultimap() {

  ImmutableSetMultimap<Object, String> map =
      BiStream.of(1, asList("one", "one", "uno"))
          .collect(flatteningToImmutableSetMultimap(List::stream));
  assertThat(map).containsExactly(1, "one", 1, "uno");
}