ClickHouse/tests/integration/test_config_substitutions/configs/config_allow_databases.xml

<clickhouse>
    <users>
        <default>
            <password></password>
            <profile>default</profile>
            <quota>default</quota>
        </default>
        <test_allow>
            <password></password>
            <profile>default</profile>
            <quota>default</quota>
            <networks>
                <ip>::/0</ip>
            </networks>
            <allow_databases>
                <database>default</database>
            </allow_databases>
        </test_allow>
    </users>
</clickhouse>