assertEquals(original, copy);
    assertTrue(copy instanceof ImmutableMultiset);
    return copy;
  }

  @CanIgnoreReturnValue
  @GwtIncompatible // SerializableTester
  static <E> Collection<E> reserializeAndAssertElementsEqual(Collection<E> original) {
    Collection<E> copy = reserialize(original);
    assertTrue(elementsEqual(original, copy));
    assertTrue(copy instanceof ImmutableCollection);
    return copy;
  }