Capybara + rails: how to get the id of a newly created record

    test 'create a standard po with items' do

      po_count = PurchaseOrder.count

      visit new_purchase_order_path
      page.select po.supplier.name, from: 'purchase_order_supplier_id'
      page.select po.company_profile.name, from: 'purchase_order_company_profile_id'
      page.select po.delivery_site.name, from: 'purchase_order_delivery_site_id'
      page.click_button 'purchase_order_submit'

      page.has_content? 'PurchaseOrder was successfully created.'
      assert_equal po_count + 1, PurchaseOrder.count
      
      #How can I get the newly created po....
      po = ?

    #adding items
      page.click_link 'Add items to this purchase order'
      #select all
      assert_equal 0, PurchasedItem.where(purchase_order_id: po.to_param).count
      page.all("table#new_purchased_items input[type='checkbox']").each{|cb| page.check(cb[:id])}
      page.click_button 'purchase_order_submit'
      #errors
      assert_equal 0, PurchasedItem.where(purchase_order_id: po.to_param).count
      page.has_content? 'error'

      page.all('table#new_purchased_items input[id$="unit_price"]').each{|ip| ip.set(3.5)}
      page.all('table#new_purchased_items input[id$="quantity"]').each{|ip| ip.set(5)}
      page.click_button 'purchase_order_submit'

      assert_not_equal 0, PurchasedItem.where(purchase_order_id: po.to_param).count
    end