public function testCountMonthsNotOverlapped()
 {
     $unit = IntervalUnit::create('month');
     $this->assertEquals(4, $result = $unit->countInRange(TimestampRange::create($start = Timestamp::create('2008-12-31 23:59:58'), $end = Timestamp::create('2009-05-28 03:00:00')), false));
     $this->assertLessThanOrEqual($end->toStamp(), $start->spawn($result . ' ' . $unit->getName())->toStamp());
 }