luhn_test.rb

require 'test/unit'

class LuhnTest < Test::Unit::TestCase
  
  def luhn_valid?(s)
    return false unless s && s.is_a?(String)
    return false if s.empty?
    value = s.gsub(/\D/, '')
    return false if value.empty?
    value.
      reverse.
      each_char.
      collect(&:to_i).
      each_with_index.
      inject(0) {| num, (i, index) |
        num + if (index + 1) % 2 == 0
          i*=2; ((i > 9) ? (i % 10) + 1 : i)
        else
          i
        end
      } % 10 == 0
  end
  
  def test_nil_or_empty_string
    check_invalid nil
    check_invalid ""
  end
  
  def test_no_digits_is_not_valid
    check_invalid "foo"
  end
  
  def test_should_not_be_valid
    # 0  1  2  3  4  5  6  7  8  9
    # 0  1  4  3  8  5  12 7  16
    #--------------------------
    # 0 + (1) + (4) + (3) + (8) + (5) + (1+2) + (7) + (1+6) + 9 = 47 % 10 = 7 NOT VALID 
    check_invalid '0123456789'
    
    # 1  2  3  4  5  6  7  8  9
    # 1  4  3  8  5  12 7  16
    #--------------------------
    # (1) + (4) + (3) + (8) + (5) + (1+2) + (7) + (1+6) + 9 = 47 % 10 = 7 NOT VALID 
    check_invalid '123456789'
    
    # 1  2  0  2  3  4  5  6  7  8  8  1
    # 1  4  0  2  6  4  10 6  14 8  16
    #-----------------------------------
    # (1) + (4) + (0) + (2) + (6) + (4) + (1+0) + (6) + (1+4) + (8) + (1+6) + 1 = 45 % 10 = 5 NOT VALID 
    check_invalid '1 2 0 2 3 4 5 6 7 8 9 1'
    
  end
  
  def test_should_be_valid
    # 9  3  8  9  7  0  2  3  5  9
    # 18 3  16 9  14 0  4  3  10
    #-----------------------------
    # (1+8) + 3 + (1+6) + 9 + (1+4) + 0 + 4 + 3 + (1+0) + 9 = 50 % 10 VALID
    check_valid '9389702359'
    check_valid '9389 702 359' 
    check_valid '9389 - 702 - 359' 
    
    # 5  1  0  5  1  0  5  1  0  5  1  0  5  1  0  0
    # 10 1  0  5  2  0  10 1  0  5  2  0  10 1  0 
    #-----------------------------------------------
    # (1+0) + 1 + 0 + 5 + 2 + 0 + (1+0) + 0 + 5 + 2 + (1+0) + 1 + 0 +  = 20 % 10 = 0 VALID
    check_valid '5105 1051 0510 5100' 
    
    # 3 4 0 0 0 0 0 0 0 0 0 0 0 0 9
    # 3 8 0 0 0 0 0 0 0 0 0 0 0 0
    #--------------------------
    # (3) + (8) + a whack load of zeros + 9 = 20 % 0 = VALID
    check_valid '3400 0000 0000 009'
    
    # 3  7  0  0  0  0  0  0  0  0  0  0  0  0  2 
    # 3  14 0  0  0  0  0  0  0  0  0  0  0  0
    #-----------------------------------
    # 3 + (1 + 4) + 2 = 10 % 10 = 0 VALID! 
    check_valid '3700 0000 0000 002'
  end
  
  def check_valid(string)
    assert luhn_valid?(string), "INVALID: #{string} (should be valid)"
  end
  
  def check_invalid(string)
    assert !luhn_valid?(string), "VALID: #{string} (should be invalid)"
  end
end