magento-test/app/code/Magento/SalesRule/Test/Mftf/ActionGroup/StorefrontApplyDiscountCodeActionGroup.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">
    <!-- Apply discount code during checkout -->
    <actionGroup name="StorefrontApplyDiscountCodeActionGroup">
        <arguments>
            <argument name="discountCode" type="string"/>
        </arguments>
        <conditionalClick selector="{{DiscountSection.DiscountTab}}" dependentSelector="{{DiscountSection.CouponInput}}" visible="false" stepKey="clickToAddDiscount"/>
        <fillField selector="{{DiscountSection.DiscountInput}}" userInput="{{discountCode}}" stepKey="fillFieldDiscountCode"/>
        <click selector="{{DiscountSection.ApplyCodeBtn}}" stepKey="clickToApplyDiscount"/>
        <waitForElementVisible selector="{{DiscountSection.DiscountVerificationMsg}}" time="30" stepKey="waitForDiscountToBeAdded"/>
        <see selector="{{DiscountSection.DiscountVerificationMsg}}" userInput="Your coupon was successfully applied" stepKey="assertDiscountApplyMessage"/>
    </actionGroup>
</actionGroups>