public function testYearBoundary()
{
$startDate = new \DateTime('2015-12-20', new \DateTimeZone('America/New_York'));
$result = Yasumi::nextWorkingDay('USA', $startDate, 20);
/**
* 20 working days between 20th Dec and 20th Jan
* 2015-12-20 is a Sunday
* 21st - 24th (4 Workdays)
* 25th Christmas, 26th-27th Weekend
* 28th - 31st (4 Workdays)
* 1st Jan New Years, 2nd-3rd Weekend
* 4th - 8th (5 Workdays)
* 9th-10th Weekend
* 11th-15th (5 Workdays)
* 16th-17th Weekend, 18th Martin Luther King Day
* 19th-20th (2 Workdays)
*
* @see https://www.timeanddate.com/calendar/?year=2016&country=1
*/
$this->assertEquals('2016-01-20', $result->format('Y-m-d'));
$startDate = new \DateTime('2016-01-20', new \DateTimeZone('America/New_York'));
$result = Yasumi::prevWorkingDay('USA', $startDate, 20);
$this->assertEquals('2015-12-18', $result->format('Y-m-d'));
}