public async Task <double> Apply(double amount, string postalCode)
        {
            // Logic is as simple as possible because the goal is to explore the testing options, not the complexity of the problem.
            var response = await _locationClient.GetDetails(postalCode);

            if (response.Province == "QC")
            {
                return(amount * QuebecTaxRate);
            }
            else
            {
                return(amount * RestOfCanadaTaxRate);
            }
        }