JeroenDesloovere\VCard\VCard::addBirthday PHP Method

    public function addBirthday($date)
    {
        $this->setProperty('birthday', 'BDAY', $date);
        return $this;
    }

 public function testBDay()
 {
     $vcard = new VCard();
     $vcard->addBirthday('31-12-2015');
     $parser = new VCardParser($vcard->buildVCard());
     $this->assertEquals($parser->getCardAtIndex(0)->birthday->format('Y-m-d'), '2015-12-31');
 }