test.php

<?php

define('CLI_SCRIPT', true);
require_once('config.php');


function check($year, $day) {
    $calendartype = \core_calendar\type_factory::get_calendar_instance();

    $timestamp = $calendartype->convert_to_timestamp(
            $year,
            1,
            $day
        );
    $time = $calendartype->timestamp_to_date_array($timestamp);

    $prevmonthyear = $calendartype->get_prev_month($time['year'], $time['mon']);
    $prev = $calendartype->convert_to_timestamp(
            $prevmonthyear[1],
            $prevmonthyear[0],
            1
        );
    $prevtime = $calendartype->timestamp_to_date_array($prev);

    $nextmonthyear = $calendartype->get_next_month($time['year'], $time['mon']);
    $next = $calendartype->convert_to_timestamp(
            $nextmonthyear[1],
            $nextmonthyear[0],
            1
        );
    $nexttime = $calendartype->timestamp_to_date_array($next);

    if ($time['mon'] == 1) {
        if ($prevtime['mon'] != 12) {
            echo "== " . __LINE__ . " ======================================================================\n";
            print_object($prevtime);
            print_object($time);
            print_object($nexttime);
            echo "============================================================================\n";
        }
    } else {
        if ($time['mon'] != $prevtime['mon'] + 1) {
            echo "== " . __LINE__ . " ======================================================================\n";
            print_object($prevtime);
            print_object($time);
            print_object($nexttime);
            echo "============================================================================\n";
            die;
        }
    }
    if ($time['mon'] == 12) {
        if ($nexttime['mon'] != 1) {
            echo "== " . __LINE__ . " ======================================================================\n";
            print_object($prevtime);
            print_object($time);
            print_object($nexttime);
            echo "============================================================================\n";
        }
    } else {
        if ($time['mon'] != $nexttime['mon'] - 1) {
            echo "== " . __LINE__ . " ======================================================================\n";
            print_object($prevtime);
            print_object($time);
            print_object($nexttime);
            echo "============================================================================\n";
        }
    }
}

for ($year = 1970; $year < 2200; $year++) {
    echo "\n == {$year} ==\n\n";
    for ($day = 1; $day < 366; $day++) {
        check($year, $day);
    }
}
echo "\n";