public function test_isoWeekDate_basics()
 {
     $this->assertEquals(DateTimeFormatter::ISO_WEEK_DATE()->getChronology(), IsoChronology::INSTANCE());
     $this->assertEquals(DateTimeFormatter::ISO_WEEK_DATE()->getZone(), null);
     $this->assertEquals(DateTimeFormatter::ISO_WEEK_DATE()->getResolverStyle(), ResolverStyle::STRICT());
 }