magento-test/app/code/Magento/MediaGalleryUi/Test/Mftf/ActionGroup/AssertImageAddedToPageContentActionGroup.xml

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

<actionGroups xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xsi:noNamespaceSchemaLocation="urn:magento:mftf:Test/etc/actionGroupSchema.xsd">
    <actionGroup name="AssertImageAddedToPageContentActionGroup">
        <annotations>
            <description>Validates that the an image was added to the content.</description>
        </annotations>
        <arguments>
            <argument name="imageName" type="string"/>
        </arguments>
       <grabValueFrom selector="{{CmsNewPagePageContentSection.content}}"  stepKey="grabTextFromContent"/>
        <assertStringContainsString stepKey="assertContentContainsAddedImage">
            <expectedResult type="string">{{imageName}}</expectedResult>
            <actualResult type="variable">grabTextFromContent</actualResult>
        </assertStringContainsString>
    </actionGroup>
</actionGroups>