purchase = self.create_purchase(self.product_fifo,
                                        quantity=13.0,
                                        unit=self.unit_ton,
                                        unit_price=Decimal(1000), invoice_method='shipment')

        shipment = self.supplier_shipment_ship(purchase)

        for invoice in purchase.invoices:
            invoice.invoice_date = datetime.date.today()
            invoice.save()

        invoice, = purchase.invoices

        Model.get('account.invoice').validate_invoice([invoice.id for invoice in purchase.invoices], self.current_config.context)

        invoice_line = Model.get('account.invoice.line').find()[0]
        self.assertEquals(invoice_line.invoice, invoice)
        self.assertEquals(invoice.currency, self.currency)
        invoice_line.quantity = Decimal('12.')
        invoice_line.save()