odoo16/addons/mail/tests/test_mail_template.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <record id="mail_template_test_attachment" model="ir.attachment">
        <field name="datas">bWlncmF0aW9uIHRlc3Q=</field>
        <field name="name">YourCompany2022.doc</field>
    </record>

    <record id="mail_template_test" model="mail.template">
        <field name="name">Mail: Test Mail Template</field>
        <field name="model_id" ref="base.model_res_users"/>
        <field name="email_from">"{{ object.company_id.name }}" &lt;{{ (object.company_id.email or user.email) }}&gt;</field>
        <field name="email_to">{{ object.email_formatted }}</field>
        <field name="body_html" type="html">
            <div>Hello Odoo</div>
        </field>
        <field name="lang">{{ object.lang }}</field>
        <field name="attachment_ids" eval="[(6, 0, [ref('mail_template_test_attachment')])]"/>
    </record>
</odoo>