Write a class with a method that takes a number as an input and calculates the sum of its digits, until there is a single digit answer. Include the tests.

For examples:

• When receiving 16 as a parameter it returns 7 (16 --> 1 + 6)
• When receiving 942 as a parameter it returns 6 (942 --> 9 + 4 + 2 = 15 --> = 1 + 5 = 6)
• When receiving 99999999999 as a parameter it returns 9 (99999999999 --> 9 + 9 + 9 + 9 + 9 + 9 + 9 + 9 + 9 + 9 + 9 = 99 --> = 9 + 9 = 18 --> = 1 + 8 = 9)

In order to solve the described problem I created the following structure and files:

• Gemfile - I have added rspec for specs and require_all gem used to require entire folders when needed.
• /bin - Having the executable file used to run it from the console + a small validation of the input
• /lib - Containing actually the sum_of_digits_calculator.rb used to provide us the sing digits sum of the input number
• /rspec - Containing the specs to validate the implementation

1. I have restricted the input passed to the calculator to be a positive integer (including 0). Didn;'t created a separate validator as was not discussed or asked before.
2. I didn't used ruby build in methods like reduce(:+) as I thought are doing to much complex for what we need
   • This could have been a different implementation using reduce

       def self.calculate_sum(num)
         return num if num < 10
     
         sum = num.to_s.split('').map(&:to_i).reduce(:+)
     
         self.calculate_sum(sum)
       end

> bin/sum_of_digits <number> or ruby bin/sum_of_digits <number> in case permision denied.

> rspec spec