Update Spec to force AJAX Error

Specs did not catch the deprecated method "error" because there were
not any tests that checked for an AJAX error. Added steps to a current
current test to ensure an AJAX call fails to cover the method "fail"
and "then" incase those methods might be deprecated in the future

backend/spec/features/admin/orders/shipments_spec.rb

@@ -157,6 +157,12 @@ def ship_shipment
         page.driver.browser.switch_to.alert.accept
         find('.select2-container').click
         find(:xpath, '//body').all('.select2-drop li.select2-result', text: "#{location_name} (0 on hand)")[1].click
+        find('#item_quantity').fill_in(with: 'text')
+        find('.save-split').click
+        alert_text = page.driver.browser.switch_to.alert.text
+        expect(alert_text).to include 'Quantity must be greater than 0'
+        page.driver.browser.switch_to.alert.accept
+        find('#item_quantity').fill_in(with: '1')
         find('.save-split').click
       end
       expect(page).to have_content /Pending package from '#{location_name}'/i