return String.valueOf(input);
                        }
                      });
        });
  }

  public void testCopyInto_list() {
    assertThat(fluent(1, 3, 5).copyInto(Lists.newArrayList(1, 2)))
        .containsExactly(1, 2, 1, 3, 5)
        .inOrder();
  }

  public void testCopyInto_set() {