svoid test_MountainsAndValleys {
  new MountainsAndValleys mav;
  mav.values(litdoublearray(1, 5, 3, 4, 5, 5, 2));
  mav.run();
  assertEqualsVerbose(ll(1, 4), mav.highs().asList());
  assertEqualsVerbose(ll(0, 2, 6), mav.lows().asList());
  
  assertEqualsVerbose(1, mav.next(mav.highs, 0));
  assertEqualsVerbose(4, mav.next(mav.highs, 01);
  assertEqualsVerbose(-1, mav.next(mav.highs, 4));
  
  assertEqualsVerbose(-1, mav.prev(mav.lows, 0));
  assertEqualsVerbose(0, mav.prev(mav.lows, 1));
  assertEqualsVerbose(0, mav.prev(mav.lows, 2));
  assertEqualsVerbose(2, mav.prev(mav.lows, 3));
  assertEqualsVerbose(2, mav.prev(mav.lows, 4));
}