magento-test/app/code/Magento/Customer/Test/Mftf/ActionGroup/StorefrontFillBillingAddressActionGroup.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="StorefrontFillBillingAddressActionGroup">
      <arguments>
          <argument name="address" defaultValue="CustomerUKAddress" type="entity"/>
      </arguments>
        <fillField selector="{{CheckoutPaymentSection.guestFirstName}}" userInput="{{address.firstname}}" stepKey="enterFirstName"/>
        <fillField selector="{{CheckoutPaymentSection.guestLastName}}" userInput="{{address.lastname}}" stepKey="enterLastName"/>
        <fillField selector="{{CheckoutPaymentSection.guestStreet}}" userInput="{{address.street[0]}}" stepKey="enterStreet"/>
        <fillField selector="{{CheckoutPaymentSection.guestCity}}" userInput="{{address.city}}" stepKey="enterCity"/>
        <fillField selector="{{CheckoutPaymentSection.guestPostcode}}" userInput="{{address.postcode}}" stepKey="enterPostcode"/>
        <selectOption selector="{{CheckoutPaymentSection.guestCountry}}" userInput="{{address.country_id}}" stepKey="enterCountry"/>
        <fillField selector="{{CheckoutPaymentSection.guestTelephone}}" userInput="{{address.telephone}}" stepKey="enterTelephone"/>
        <waitForLoadingMaskToDisappear stepKey="waitForLoadingMask"/>
    </actionGroup>
</actionGroups>