assertThrows(IllegalArgumentException.class, () -> Range.atMost(2).gap(Range.atMost(1)));
  }

  public void testGap_connectedAdjacentYieldsEmpty() {
    Range<Integer> range = Range.open(3, 4);

    assertEquals(Range.closedOpen(4, 4), range.gap(Range.atLeast(4)));
    assertEquals(Range.openClosed(3, 3), range.gap(Range.atMost(3)));
  }