Intro to TDD

calculator.rb

class Calculator
  attr_reader :string_to_calculate

  def initialize(string_to_calculate, options = {})
    @string_to_calculate = string_to_calculate
    @delimiter = options[:delimiter]
  end

  def add
    raise ArgumentError, error_message unless negatives.empty?
    numbers.reject { |x| x > 1000 }.reduce(0, :+)
  end

  def self.add(string, options = {})
    new(string, options).add
  end

private

  def delimiter
    @regex_delimiter ||= Regexp.new("[,\\n#{Regexp.escape(@delimiter.to_s)}]")
  end

  def numbers
    @numbers ||= string_to_calculate.split(delimiter).map(&:to_i)
  end

  def negatives
    @negatives ||= numbers.select { |n| n < 0 }
  end

  def error_message
    "negatives are not allowed: #{negatives.join(", ")}"
  end
end

calculator_test.rb

gem 'minitest'
require "minitest/autorun"
require_relative "calculator"

class TestCalculator < Minitest::Test
  def test_given_a_string_returns_a_number
    number = rand(100)
    assert_equal number, Calculator.add(number.to_s)
  end

  def test_empty_string_returns_zero
    assert_equal 0, Calculator.add("")
  end

  def test_csv_should_sum_values
    n1 = rand(100)
    n2 = rand(100)
    assert_equal n1 + n2, Calculator.add("#{n1},#{n2}")
  end

  def random_nuber_array(min, max)
    numbers = Array.new((min..max).to_a.sample) { |x| rand(100) }
  end

  def test_greater_than_two_numbers_sum_values
    assert_equal 10, Calculator.add("1,3,5,1")

    numbers = random_nuber_array(2, 50)
    sum = 0
    numbers.each { |x| sum += x }

    assert_equal sum , Calculator.add(numbers.join(","))
  end

  def test_newline_as_delimeter_when_summing_values
    ["1\n2,3", "1\n2\n3"].each do |number_string|
      assert_equal 6, Calculator.add(number_string)
    end
  end

  def test_negative_number_throws_error
    [
      { input: "-1", error: "-1" },
      { input: "1,2,-5", error: "-5" },
      { input: "-1,-2,-3", error: "-1, -2, -3" },
      { input: "-1,22,-3", error: "-1, -3" },
    ].each do |test|
      err = assert_raises ArgumentError do
        Calculator.add(test[:input])
      end

      assert_equal "negatives are not allowed: " + test[:error], err.message
    end
  end

  def test_ignore_numbers_greater_than_1000
    [
      { input: "1001", sum: 0 },
      { input: "1001,2", sum: 2 },
      { input: "1000,2", sum: 1002 },
      { input: "1002,10", sum: 10 },
      { input: "5,1020,7", sum: 12 }
    ].each do |test|
      assert_equal test[:sum], Calculator.add(test[:input])
    end
  end

  def test_user_specified_delimiter
    ["+", "|", ".", "]"].each do |delimiter|
      assert_equal 6, Calculator.add([1, 2, 3].join(delimiter), delimiter: delimiter)
    end
  end

  def test_custom_delimiter_with_default_delimiters
    assert_equal 10, Calculator.add("1,2+3\n4", delimiter: "+")
  end
end