Testing the WeekNumber class

week_number.rb

# encoding: utf-8

class WeekNumber
  attr_reader :cweek, :year

  def initialize(cweek = Date.today.cweek, year = Date.today.year)
    @year  = year.to_i
    @cweek = cweek.to_i

    if @cweek > WeekNumber.weeks_in(@year)
      raise ArgumentError, 'Invalid cweek'
    end
  end

  def self.weeks_in(year)
    Date.new(year, 12, 28).cweek # magick date!
  end

  def self.by_date(date)
    new date.cweek, date.year
  end

  def self.by_key(key)
    new(*key.split('v').reverse)
  end

  def key
    "#{year}v#{cweek}"
  end

  def label
    "Vecka #{cweek} #{year}"
  end
end

week_number_spec.rb

# encoding: utf-8

require_relative "spec_helper"
require_relative "../lib/week_number.rb"

describe WeekNumber do
  subject { WeekNumber }

  let(:today)           { Date.today   }
  let(:future)          { today + 1337 }
  let(:year)            { today.year   }
  let(:cweek)           { today.cweek  }
  let(:weeks_this_year) { Date.new(today.year, 12, 28).cweek }
  let(:current_key)     { "#{year}v#{cweek}" }
  let(:current_label)   { "Vecka #{cweek} #{year}" }

  it "doesn’t allow invalid week numbers" do
    -> { subject.new(weeks_this_year + 1) }.must_raise ArgumentError
  end

  it "returns a key for a given week" do
    subject.new(1).key.must_equal "#{year}v1"
    subject.new(2,1990).key.must_equal "1990v2"
    subject.new.key.must_equal current_key
  end

  it "returns a label for a given week" do
    subject.new(1).label.must_equal "Vecka 1 #{year}"
    subject.new(2,1990).label.must_equal "Vecka 2 1990"
    subject.new.label.must_equal current_label
  end

  it "returns the key for today" do
    subject.by_date(today).key.must_equal current_key
  end

  it "returns the key for a date in the future" do
    subject.by_date(future).key.must_equal "#{future.year}v#{future.cweek}"
  end

  it "returns a label for a given key" do
    subject.by_key(current_key).label.must_equal current_label
    subject.by_key('1999v52').label.must_equal "Vecka 52 1999"
  end
end