assertSame(immutableList, Iterables.unmodifiableIterable(immutableList));
    assertSame(immutableList, Iterables.unmodifiableIterable((List<String>) immutableList));
  }

  public void testFrequency_multiset() {
    Multiset<String> multiset = ImmutableMultiset.of("a", "b", "a", "c", "b", "a");
    assertEquals(3, frequency(multiset, "a"));
    assertEquals(2, frequency(multiset, "b"));