magento-test/app/code/Magento/Checkout/Test/Mftf/ActionGroup/StorefrontFillOptionFieldInputActionGroup.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="StorefrontFillOptionFieldInputActionGroup">
        <annotations>
            <description>Fills in the provided Option Title with the provided Value on a Storefront product page.</description>
        </annotations>
        <arguments>
            <argument name="optionTitle" defaultValue="ProductOptionField"/>
            <argument name="fieldInput" type="string"/>
        </arguments>
        
        <fillField selector="{{StorefrontProductInfoMainSection.productOptionFieldInput(optionTitle.title)}}" userInput="{{fieldInput}}" stepKey="fillOptionField"/>
    </actionGroup>
</actionGroups>