test.php

<?php
public function getNumberOfPublicHolidaysForPeriod() {
    if(!$this->numberOfPublicHolidaysInPeriod) {
      $this->numberOfPublicHolidaysInPeriod = PublicHoliday::getNumberOfPublicHolidaysForPeriod(
        $this->period->start_date,
        $this->period->end_date
      );
    }

    return $this->numberOfPublicHolidaysInPeriod;
  }