test.rb

ENV['BUNDLE_GEMFILE'] = File.expand_path('../../rails/Gemfile', __FILE__)
require_relative '../rails/load_paths'
require 'active_record'
require 'active_support/all'
require 'minitest/autorun'

ActiveRecord::Base.establish_connection(adapter: :sqlite3, database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :business_units do |t|
    t.string :reference
    t.timestamps
  end

  create_table :worksites do |t|
    t.string :reference
    t.timestamps
  end

  create_table :worksites_business_units do |t|
    t.string :reference
    t.belongs_to :business_unit, null: false
    t.belongs_to :worksite, null: false
    t.timestamps
  end
end

class BusinessUnit < ActiveRecord::Base
  has_many :worksites, :through => :worksites_business_units
  has_many :worksites_business_units
end

class Worksite < ActiveRecord::Base
  belongs_to :postal_address
  has_many :business_units, :through => :worksites_business_units
  has_many :worksites_business_units
end

class WorksitesBusinessUnit < ActiveRecord::Base
  belongs_to :worksite
  belongs_to :business_unit
end

class WorksiteTest < ActiveSupport::TestCase
  def test_save_callbacks_on_has_many_through_when_only_one_side_is_new
    bu = BusinessUnit.new(reference: '123')
    ws = Worksite.new(reference: '456')
    ws.business_units << bu
    ws.save!
    assert_equal 1, ws.business_units.count
  end
end