def METHOD_NAME():
    user = create_new_user()
    default_domain = SLDomain.filter_by(hidden=False).order_by(SLDomain.order).first()
    user.default_alias_public_domain_id = default_domain.id
    Session.flush()
    options = AliasOptions(
        show_sl_domains=True, show_partner_domains=get_proton_partner()
    )
    suffixes = get_alias_suffixes(user, alias_options=options)
    found_default = False
    found_domains = set()
    for suffix in suffixes:
        assert suffix.domain not in found_domains
        found_domains.add(suffix.domain)
        if default_domain.domain == suffix.domain:
            found_default = True
    assert found_default