Braintree\PaymentMethodGateway::createSignature PHP Method

    public static function createSignature()
    {
        $signature = array_merge(self::baseSignature(), ['customerId']);
        return $signature;
    }

 public function testCreateSignature()
 {
     $expected = ['billingAddressId', 'cardholderName', 'cvv', 'deviceData', 'expirationDate', 'expirationMonth', 'expirationYear', 'number', 'paymentMethodNonce', 'token', ['options' => ['failOnDuplicatePaymentMethod', 'makeDefault', 'verificationMerchantAccountId', 'verifyCard']], ['billingAddress' => Braintree\AddressGateway::createSignature()], 'customerId'];
     $this->assertEquals($expected, Braintree\PaymentMethodGateway::createSignature());
 }