magento-test/setup/performance-toolkit/config/di.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\Framework\Mail\TransportInterface" type="Magento\Setup\Framework\Mail\TransportInterfaceMock"/>
    <preference for="Magento\Framework\Mail\Template\TransportBuilder" type="Magento\Setup\Framework\Mail\Template\TransportBuilderMock"/>
</config>