Getting rid of wait_for_it in http://blog.arkency.com/2015/09/testing-race-conditions/

threads.rb

threads = concurrency_level.times.map { |i|
  -> {
    Thread.new do
      begin
        customers[i].buy_products([{quantity: 1, product: product}])
      rescue Orders::CreateOrderService::Invalid
        fail_occurred = true
      end
    end
  }
}.map(&:call)

# We don't even need threads variable now!

concurrency_level.times.map { |i|
  -> {
    Thread.new do
      begin
        customers[i].buy_products([{quantity: 1, product: product}])
      rescue Orders::CreateOrderService::Invalid
        fail_occurred = true
      end
    end
  }
}.map(&:call).map(&:join)