actual result

 Calendar buddhist
 Calendar chinese
int(1)
int(1)
 Calendar coptic
 Calendar dangi
int(1)
int(1)
 Calendar ethiopic
 Calendar ethiopic-amete-alem
 Calendar gregorian
 Calendar hebrew
 Calendar indian
int(0)
int(0)
 Calendar islamic
 Calendar islamic-civil
 Calendar islamic-umalqura
 Calendar islamic-tbla
 Calendar iso8601
 Calendar japanese
 Calendar persian
int(0)
int(0)
 Calendar roc

expected result

 Calendar buddhist
 Calendar chinese
 Calendar coptic
 Calendar dangi
 Calendar ethiopic
 Calendar ethiopic-amete-alem
 Calendar gregorian
 Calendar hebrew
 Calendar indian
 Calendar islamic
 Calendar islamic-civil
 Calendar islamic-umalqura
 Calendar islamic-tbla
 Calendar iso8601
 Calendar japanese
 Calendar persian
 Calendar roc

testfile.php

<?php

// The implementation of the chinese calendar seems to be broken
// The months can not be set.
$calendars = [
 "buddhist",
            "chinese",
            "coptic",
            "dangi",
            "ethiopic",
            "ethiopic-amete-alem",
            "gregorian",
            "hebrew",
            "indian",
            "islamic",
            "islamic-civil",
            "islamic-umalqura",
            "islamic-tbla",
            "iso8601",
            "japanese",
            "persian",
            "roc",
];
foreach ($calendars as $calendar) {

	echo ' Calendar ' . $calendar . PHP_EOL;
	$f = IntlCalendar::createInstance('UTC', '@calendar=' . $calendar);
	$i = $f->get(IntlCalendar::FIELD_MONTH);
	$f->set(IntlCalendar::FIELD_MONTH, 0);
	if ($i == $f->get(IntlCalendar::FIELD_MONTH)) {
		var_dump($i, $f->get(IntlCalendar::FIELD_MONTH));
	}
}