LoriCreditCard3ref.rb

class CreditCard

  def validate(value)
    card_num = value.to_s
    
    if card_num.empty?
      false
      
    else
      card_num.chars 
        .map(&:to_i).reverse
        .map.with_index {|num, index| index.odd? ? num * 2 : num }
        .map {|num| num > 9 ? num - 9 : num }
        .reduce(:+) % 10 == 0 ? true : false
    end
  end

end

LoriCreditCard3Test.rb

require 'minitest/autorun'
require 'minitest/pride'
require_relative 'credit_card3'

class CreditCardTest < Minitest::Test 

  def setup
    @card_num = CreditCard.new
  end

  def test_empty_string_is_invalid_credit_card
    
    result = @card_num.validate("")
    refute result
  end

  def test_zero_is_valid_credit_card
    
    result = @card_num.validate("0")
    assert result
  end

  def test_one_is_not_a_valid_credit_card

    result = @card_num.validate("1")
    refute result
  end

  def test_42_is_not_a_valid_credit_card
    
    result = @card_num.validate("42")
    assert result
  end

  def test_42_integer_is_a_valid_credit_card
    
    result = @card_num.validate(42)
    assert result
  end

  def test_4242_is_a_valid_credit_card
    
    result = @card_num.validate("4242")
    assert result
  end

  def test_59_is_a_valid_credit_card
    
    result = @card_num.validate("59")
    assert result
  end
  
  def test_4024007106512380_integer_is_a_invalid_credit_card
    
    result = @card_num.validate(4024007106512380)
    refute result
  end

  def test_5541801923795240_integer_is_a_invalid_credit_card
    
    result = @card_num.validate(5541801923795240)
    refute result
  end
  
  def test_6011797668868728_integer_is_a_invalid_credit_card
    
    result = @card_num.validate(6011797668868728)
    refute result
  end

  def test_5541808923795240_integer_is_a_valid_credit_card
    
    result = @card_num.validate(5541808923795240)
    assert result
  end

  def test_4024007136512380_integer_is_a_valid_credit_card
    
    result = @card_num.validate(4024007136512380)
    assert result
  end

  def test_6011797668868728_integer_is_a_valid_credit_card

    result = @card_num.validate(6011797668867828)
    assert result
  end

  def test_amex_card_342804633855673_is_a_valid_credit_card

    result = @card_num.validate(6011797668867828)
    assert result
  end

  def test_amex_card_342801633855673_is_an_invalid_string_credit_card
    
    result = @card_num.validate("342801633855673")
    refute result
  end

end