newsupernova/dev/tests/api-functional/_files/Magento/TestModuleMSC/etc/extension_attributes.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
    <extension_attributes for="Magento\TestModuleMSC\Api\Data\ItemInterface">
        <attribute code="custom_attribute_data_object" type="Magento\TestModuleMSC\Api\Data\CustomAttributeDataObjectInterface" />
        <attribute code="custom_attribute_string" type="string" />
    </extension_attributes>
    <extension_attributes for="Magento\TestModuleMSC\Api\Data\CustomAttributeDataObjectInterface">
        <attribute code="custom_attribute_nested" type="Magento\TestModuleMSC\Api\Data\CustomAttributeNestedDataObjectInterface" />
        <attribute code="custom_attribute_int" type="int" />
    </extension_attributes>
</config>