blog-post-830-plan-v1

plan.rb

class Plan < ActiveRecord::Base
  has_many :members
  validates :name, presence: true

  BASE_PRICE = 20
  DISCOUNT = 1

  # Apply discount if has more than 2 members
  def price
    if members.count > 2
      BASE_PRICE - discount
    else
      BASE_PRICE
    end
  end

  private

  def discount
    (members.count - 2) * DISCOUNT
  end
end

plan_spec.rb

require 'rails_helper'

RSpec.describe Plan, type: :model do
  describe ".price"  do
    let(:plan) { Plan.create(name: 'basic') }

    describe "has less than 2 members"  do
      let(:dan) { Member.create(first_name: 'Daniel') }
      let(:tom) { Member.create(first_name: 'Thomas') }

      it "should return base price when one member" do
        plan.members << dan
        expect(plan.price).to eql(20)
      end

      it "should return base price when two members" do
        plan.members << dan
        plan.members << tom
        expect(plan.price).to eql(20)
      end
    end

    describe "has more than two members"  do
      let(:joe) { Member.create(first_name: 'Joe') }
      let(:mary) { Member.create(first_name: 'Mary') }
      let(:sarah) { Member.create(first_name: 'Sarah') }

      it "should give 1 discount per additional user"  do
        plan.members << joe
        plan.members << mary
        plan.members << sarah
        expect(plan.price).to eql(19)
      end
    end
  end
end