ARGOMENTO: TEST Unit su OnChange: errore o bug ??

class ResPartner(models.Model):
    """ Extends res.partner to add Italian Fiscal Code
    """
    # Private attributes
    _inherit = 'res.partner'

#…. omissis

    # Fields declaration
    fiscalcode = fields.Char(
        'Fiscal Code', size=16, help="Italian Fiscal Code")
    is_soletrader = fields.Boolean(
        string='Sole Trader',
        default=False,
        readonly=False,
        help="Checked if company is a sole trader")

#… omissis
    @api.multi
    @api.onchange('fiscalcode', 'parent_id')
    def onchange_fiscalcode(self):
        """ Partners not in same parent/child relationship should
        have different fiscal code.
        A proper warning is displayed.
        """
        set_trace()
        self.ensure_one()

        if not self.fiscalcode:
            # fiscalcode empty
            return {}
        # search any partner with same fiscal code in this compamy
        same_fiscalcode_partners = self.env['res.partner'].search([
            ('fiscalcode', '=', self.fiscalcode),
            ('fiscalcode', '!=', False),
            ('company_id', '=', self.company_id.id),
            ])
        if not same_fiscalcode_partners:
            # there is no partner with same fiscalcode.
            # Safe condition. return
            return {}

        if isinstance(self.id, models.NewId) and not self.parent_id:
            # new record with no parent BUT there are other partners
            # with same fiscal code
            is_fc_present = True
        else:
            # new or old record with parent
            # get first parent to start searching
            parent = self
            while parent.parent_id:
                parent = parent.parent_id
            # all partners in our family tree
            related_partners = self.env['res.partner'].search([
                ('id', 'child_of', parent.id),
                ('company_id', '=', self.company_id.id),
                ])
            # any partner with same fiscal code OUT of our family tree ?
            is_fc_present = self.env['res.partner'].search([
                ('id', 'in', same_fiscalcode_partners.ids),
                ('id', 'not in', related_partners.ids),
                ('company_id', '=', self.company_id.id),
                ])

        if is_fc_present:
            title = _('Partner fiscal code is not unique')
            message = _('WARNING:\n'
                        'Partner fiscal code must be unique per'
                        ' company except for partner with'
                        ' parent/child relationship.'
                        ' Partners with same fiscal code'
                        ' and not related, are:\n %s!') % (
                            ', '.join(x.name for x in
                                      same_fiscalcode_partners))
            result = {
                'warning': {'title': title,
                            'message': message, }, }
        else:
            result = {}
        return result

class TestPartner(TransactionCase):
    """ Each test method is run independently and the database transaction
    is rolled back after each.
    """
    def setUp(self):
        """initializes the self.env attribute The test runner will
        run then one after the other with a call to setUp() before
        each test method and a call to tearDown() after each
        """
        super(TestPartner, self).setUp()
# -------------------------------------------------------------------
    def test_partner_onchange_fiscalcode(self):
        """ Test onchange method when an existing ficsalcode
        is provided to a new partner. 
        Needed to cover >77% for codecov...  :-( 
        """
        # Get an empty recordset
        partner = self.env['res.partner']
        # Retrieve the onchange specifications
        specs = partner._onchange_spec()
        
        # create first partner with normal fiscalcode for private citizen
        parent = self.env['res.partner'].create(
            {'name': u'Test1 Private Italian Citizen',
             'email': u"foo@gmail.com",
             'is_company': True,
             'is_soletrader': True,
             'fiscalcode': u'BNZVCN32S10E573Z', })
        test1=self.env['res.partner'].search([('fiscalcode','=','BNZVCN32S10E573Z')])
        # Prepare the values to create a child record with same fiscalcode
        values = {'name': u'OnChange Test2',
                  'email': u"foo@gmail.com",
                  'is_company': False,
                  'is_soletrader': False,
                  'parent_id': parent.id,
                  'fiscalcode': u'BNZVCN32S10E573Z', }

        # Get the result of the onchange method for fiscalcode field:
        self.env.invalidate_all()
        result = partner.onchange(values, ['fiscalcode'], specs)
        # warning: This is a dictionary containing a warning message 
        # that the web client will display to the user
        warning = result.get('warning', {})
        # check onchange method produced NO warning
        self.assertTrue(warning)