instances_counter_per_class_module_spec

require 'spec_helper'

module Counter
  def self.included(base)
    base.class_eval do
      @@counters = {}

      def self.instances_count
        @@counters[self]
      end
    end
  end

  def self.reset_counters
    @@counters = {}
  end

  def initialize
    @@counters[self.class] ||= 0
    @@counters[self.class] += 1
  end
end

class Car
  include Counter
end

class Truck
  include Counter
end

class Van
  include Counter
end

describe 'Instance counter' do
  before { Counter.reset_counters }

  it 'works with car, van and truck' do
    Car.new
    Van.new
    Truck.new

    expect(Car.instances_count).to eq(1)
    expect(Van.instances_count).to eq(1)
    expect(Truck.instances_count).to eq(1)
  end

  it 'works with 2 cars, 4 vans and 3 trucks' do
    2.times { Car.new }
    4.times { Van.new }
    3.times { Truck.new }

    expect(Car.instances_count).to eq(2)
    expect(Van.instances_count).to eq(4)
    expect(Truck.instances_count).to eq(3)
  end
end