magento-test/app/code/Magento/MediaGalleryUi/Test/Mftf/Section/AdminMediaGalleryMessagesSection.xml

<!--
 /**
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
-->
<sections xsi:noNamespaceSchemaLocation="urn:magento:mftf:Page/etc/SectionObject.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <section name="AdminMediaGalleryMessagesSection">
        <element name="success" type="text" selector=".media-gallery-container ul.messages div.message.message-success span"/>
    </section>
</sections>