magento-test/app/code/Magento/Theme/Test/Mftf/Section/StorefrontMessagesSection.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
 /**
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
-->

<sections xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:noNamespaceSchemaLocation="urn:magento:mftf:Page/etc/SectionObject.xsd">
    <section name="StorefrontMessagesSection">
        <element name="message" type="text"
                 selector="//main//div[contains(@class, 'messages')]//div[contains(@class, 'message')]/div[contains(text(), '{{var1}}')]"
                 parameterized="true"
        />
        <element name="messageByType" type="text" selector="[data-ui-id='message-{{messageType}}']" parameterized="true" />
    </section>
</sections>