gistfile1.rb

require 'active_record'
require 'minitest/autorun'

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: 'db.sqlite3')

ActiveRecord::Schema.define do
  create_table :users, force: true do |t|
    t.references :company, index: true
  end

  create_table :companies, force: true do |t|
  end

  create_table :locations, force: true do |t|
    t.references :company, index: true
  end
end

class Location < ActiveRecord::Base
  belongs_to :company
end

class Company < ActiveRecord::Base
  has_many :locations

  class Null
    def name
      'Null name'
    end

    def locations
      []
    end
  end

  def name
    'Real name'
  end
end

class User < ActiveRecord::Base
  belongs_to :company
  has_many :locations, through: :company

  def company
    super || Company::Null.new
  end
end

describe User do
  before do
    @company = Company.create
    @location = Location.create(company: @company)
  end

  describe 'when user has real company' do
    before do
      @user = User.create(company: @company)
    end

    it 'returns correct name' do
      assert_equal 'Real name', @user.company.name
    end

    it 'returns correct locations' do
      assert_equal [@location], @user.locations
      assert_equal @user.locations, @user.company.locations
    end
  end

  describe 'when user does not have company' do
    before do
      @user = User.create
    end

    it 'returns name of null company' do
      assert_equal 'Null name', @user.company.name
    end

    it 'returns locations of null company' do
      assert_equal [], @user.locations
      assert_equal [], @user.company.locations
    end
  end
end