magento-test/app/code/Magento/Customer/Test/Mftf/ActionGroup/AdminCustomerSubscribeNewsletterActionGroup/AdminSubscribeCustomerToNewslettersActionGroup.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="AdminSubscribeCustomerToNewsletters">
        <annotations>
            <description>Set checkbox "Newsletter subscribed" on "Newsletter" tab on customer edit page.</description>
        </annotations>
        <arguments>
            <argument name="websiteId" type="string" defaultValue="1"/>
        </arguments>

        <click selector="{{AdminEditCustomerInformationSection.newsLetter}}" stepKey="clickToNewsletterTabHeader"/>
        <waitForPageLoad stepKey="waitForShowNewsletterTab"/>
        <checkOption selector="{{AdminEditCustomerNewsletterSection.subscribedStatus(websiteId)}}" stepKey="subscribeToNewsletter"/>
        <click selector="{{AdminCustomerMainActionsSection.saveAndContinue}}" stepKey="saveAndContinue"/>
        <waitForPageLoad stepKey="waitForSaving"/>
        <see userInput="You saved the customer." stepKey="seeSuccessMessage"/>
    </actionGroup>
</actionGroups>