birthday-sw-v5.rb

require "minitest/autorun"
require "date"

class Person
  CURRENT_YEAR = ->{ Date.new.year }
  attr_reader :birthday

  def initialize(attributes={})
    @birthday = attributes.fetch(:birthday)
  end

  def can_drink?(year_function = CURRENT_YEAR)
    age(year_function) > 21
  end

  def age(year_function = CURRENT_YEAR)
    year_function.call - birthday.year
  end
end

describe Person do
  let(:seventy_niner) do
    Person.new birthday: Date.new(1979)
  end

  it "age is determined by their birthday" do
    seventy_niner.age(->{ 2009 }).must_equal 30
  end

  it "can drink if older than 21" do
    seventy_niner.can_drink?(->{ 2009 }).must_equal true
  end

  it "CURRENT_YEAR is today" do
    Person::CURRENT_YEAR.call.must_equal Date.new.year
  end
end