magento-test/app/code/Magento/Theme/etc/frontend/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">
    <type name="Magento\Customer\CustomerData\SectionPoolInterface">
        <arguments>
            <argument name="sectionSourceMap" xsi:type="array">
                <item name="messages" xsi:type="string">Magento\Theme\CustomerData\Messages</item>
            </argument>
        </arguments>
    </type>
    <type name="Magento\Framework\View\Element\Message\MessageConfigurationsPool">
        <arguments>
            <argument name="configurationsMap" xsi:type="array">
                <item name="default_message_identifier" xsi:type="array">
                    <item name="renderer" xsi:type="const">\Magento\Framework\View\Element\Message\Renderer\EscapeRenderer::CODE</item>
                </item>
            </argument>
        </arguments>
    </type>
    <type name="Magento\Framework\Controller\ResultInterface">
        <plugin name="result-messages" type="Magento\Theme\Controller\Result\MessagePlugin"/>
    </type>
    <type name="Magento\Framework\View\Result\Layout">
        <plugin name="asyncCssLoad" type="Magento\Theme\Controller\Result\AsyncCssPlugin" sortOrder="-20" />
        <plugin name="deferJsToFooter" type="Magento\Theme\Controller\Result\JsFooterPlugin" sortOrder="-10" />
    </type>
    <type name="Magento\Theme\Block\Html\Header\CriticalCss">
        <arguments>
            <argument name="filePath" xsi:type="string">css/critical.css</argument>
        </arguments>
    </type>
</config>