.containsExactly(0, 1);
    assertThat(symmetricDifference(newHashSet(1, 2), newHashSet(2, 3)).copyInto(newHashSet(0, 1)))
        .containsExactly(0, 1, 3);
  }

  public void testUnion_minSize() {
    assertMinSize(union(emptySet(), emptySet()), 0);
    assertMinSize(union(setSize(2), setSize(3)), 3);
    assertMinSize(union(setSize(3), setSize(2)), 3);