}

  public void testGap_general() {
    Range<Integer> openRange = Range.open(4, 8);
    Range<Integer> closedRange = Range.closed(4, 8);

    // first range open end, second range open start
    assertEquals(Range.closed(2, 4), Range.lessThan(2).gap(openRange));
    assertEquals(Range.closed(2, 4), openRange.gap(Range.lessThan(2)));

    // first range closed end, second range open start