newsupernova/dev/tests/integration/testsuite/Magento/Paypal/_files/quote_payment.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

$quote = \Magento\TestFramework\Helper\Bootstrap::getObjectManager()->create(\Magento\Quote\Model\Quote::class);
$quote->load('test01', 'reserved_order_id');

$payment = $quote->getPayment();
$payment->setMethod(\Magento\Paypal\Model\Config::METHOD_WPP_EXPRESS)
    ->setAdditionalInformation(\Magento\Paypal\Model\Express\Checkout::PAYMENT_INFO_TRANSPORT_PAYER_ID, 123);
$quote->collectTotals()->save();