Memoizing test setup

invoice_repository_test.rb

require_relative './path/to/sales_engine_test_setup'

class InvoiceRepositoryTest < Minitest::Test
  include SalesEngineTestSetup
  def setup
    super
    
    # Any additional setup needed for InvoiceRepository tests
  end
  
  # tests go here...
end

sales_engine_test_setup.rb

module SalesEngineTestSetup
  attr_reader :sales_engine
  def setup
    @@sales_engine ||= load_sales_engine_data
    @sales_engine = @@sales_engine.dup
  end
  
  private
  def load_sales_engine_data
    puts 'Loading sales engine data!!!!'
    SalesEngine.from_csv({
      :invoices => "./data/invoices.csv",
      :items     => "./data/items.csv",
      :merchants => "./data/merchants.csv",
    })
  end
end