Generate random tracking number.

        Supported services: USPS, FedEx and UPS.

        :param str service: Post service.
        :return: Tracking number.

def tracking_number(self, service: str = 'usps') -> str:
        """Generate random tracking number.

        Supported services: USPS, FedEx and UPS.

        :param str service: Post service.
        :return: Tracking number.
        """
        service = service.lower()

        if service not in ('usps', 'fedex', 'ups'):
            raise ValueError('Unsupported post service')

        services = {
            'usps': (
                '#### #### #### #### ####',
                '@@ ### ### ### US',
            ),
            'fedex': (
                '#### #### ####',
                '#### #### #### ###',
            ),
            'ups': (
                '1Z@####@##########',
            ),
        }
        mask = self.random.choice(services[service])  # type: ignore
        return self.random.custom_code(mask=mask)