magento-test/app/code/Magento/Checkout/Test/Mftf/ActionGroup/StorefrontSelectOptionMultiSelectActionGroup.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="StorefrontSelectOptionMultiSelectActionGroup">
        <annotations>
            <description>Selects the provided Product Option under the provided Product Option Title on a Storefront Product page.</description>
        </annotations>
        <arguments>
            <argument name="optionTitle" defaultValue="ProductOptionMultiSelect"/>
            <argument name="option" defaultValue="ProductOptionValueMultiSelect2.title"/>
        </arguments>
        
        <selectOption selector="{{StorefrontProductInfoMainSection.productOptionSelect(optionTitle.title)}}" userInput="{{option}}" stepKey="selectOption"/>
    </actionGroup>
</actionGroups>