I just installed a brand new version of MediaWiki from git HEAD currently at ecefa8f10821, with no extensions or special configurations. After running composer update I ran the phpunit.php and got 9 errors all pertaining to the CollationFaTest::testGetFirstLetter complaining that "An ICU collation was requested, but the intl extension is not available."
The unit test was added by @Bawolff in May 2017.