public void TestCustomAlphabetConversionUsingStandardDigits()
        {
            var alphabet = "0123456789";
            var bigInt   = BigInteger.Parse("144413047667920780076747050081956537466");

            var str = ConvertEx.ToCustomAlphabetString(bigInt, alphabet);

            str.ShouldBe("144413047667920780076747050081956537466");

            var decoded = ConvertEx.FromCustomAlphabetString(str, alphabet);

            decoded.ShouldBe(bigInt);
        }