magento-test/app/code/Magento/Email/Test/Mftf/ActionGroup/PreviewEmailTemplateActionGroup.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="PreviewEmailTemplateActionGroup" extends="FindAndOpenEmailTemplateActionGroup">
        <click selector="{{AdminEmailTemplateEditSection.previewTemplateButton}}" after="checkTemplateName" stepKey="clickPreviewTemplate"/>
        <switchToNextTab after="clickPreviewTemplate" stepKey="switchToNewOpenedTab"/>
        <seeInCurrentUrl url="{{AdminEmailTemplatePreviewPage.url}}" after="switchToNewOpenedTab" stepKey="seeCurrentUrl"/>
        <seeElement selector="{{AdminEmailTemplatePreviewSection.iframe}}" after="seeCurrentUrl" stepKey="seeIframeOnPage"/>
        <switchToIFrame userInput="preview_iframe" after="seeIframeOnPage" stepKey="switchToIframe"/>
        <waitForPageLoad after="switchToIframe" stepKey="waitForPageLoaded"/>
    </actionGroup>
</actionGroups>