public static Arbitrary<CustomInputData> ValidCustomDelimiterData()
{
    var input = from values in GetValidListOfIntegers()
                from delimiter in Arb.Generate<NonEmptyString>()
                    where IsInt(delimiter.Item) == false
                select new CustomInputData()
                {
                    Delimiter = delimiter.Get,
                    Values = values
                };
    return input.ToArbitrary();
}