Omnipay\Common\CreditCard::getNumberLastFour PHP Method

    public function getNumberLastFour()
    {
        return substr($this->getNumber(), -4, 4) ?: null;
    }

 public function testGetNumberLastFourNonDigits()
 {
     $this->card->setNumber('4000 0000 0000 12x34');
     $this->assertSame('1234', $this->card->getNumberLastFour());
 }