throws Exception {
                    closer.eventuallyClose(closeable1, closingExecutor);
                    assertThat(peeker.getDone(input1)).isSameInstanceAs("value1");
                    try {
                      peeker.getDone(input2Failed);
                      fail("Peeker should fail for failed inputs");

      hasPeeked = false;
      peekedElement = null;
      return result;
    }

    @Override
    public void remove() {
      checkState(!hasPeeked, "Can't remove after you've peeked at next");
      iterator.remove();
    }

    @Override
    @ParametricNullness
    public E peek() {
      if (!hasPeeked) {
        peekedElement = iterator.next();