Implement a Ruby program that outputs the validity of a number by applying the Luhn Checksum.
http://en.wikipedia.org/wiki/Luhn_algorithm
Please treat this as you would any other project or task you'd encounter during your daily work. This will show us how currently code, and not how you coded 6, 12 or 18 months ago. Your code should also be suitably tested.
Input:
The program should accept a single number to validate.
Output:
The program should output the input along with the validity of the number.
Examples:
With an input of 79927398713 the output should be:
79927398713 is valid.
With an input of 79927398710 the output should be:
79927398710 is not valid.