magento-test/app/code/Magento/Cms/Test/Mftf/ActionGroup/AssertCMSPageNotFoundOnStorefrontActionGroup.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="AssertCMSPageNotFoundOnStorefrontActionGroup">
        <annotations>
            <description>Validates that the 'Whoops, our bad' error message is present and correct for a Storefront CMS Page that doesn't exist.</description>
        </annotations>

        <see userInput="Whoops, our bad..." stepKey="seePageErrorNotFound"/>
    </actionGroup>
</actionGroups>