Display error messages to user for convencience

It will also help us to debug the application if the error is not
obvious.

app/controllers/split_checkout_controller.rb

@@ -36,7 +36,10 @@ class SplitCheckoutController < ::BaseController
       advance_order_state
       redirect_to_step
     else
-      flash.now[:error] ||= I18n.t('split_checkout.errors.global')
+      flash.now[:error] ||= I18n.t(
+        'split_checkout.errors.saving_failed',
+        messages: @order.errors.full_messages.to_sentence
+      )
 
       render status: :unprocessable_entity, operations: cable_car.
         replace("#checkout", partial("split_checkout/checkout")).

config/locales/en.yml

@@ -1997,6 +1997,7 @@ en:
       cancel: Back to Payment method
     errors:
       global: "Saving failed, please update the highlighted fields."
+      saving_failed: "Saving failed, please update the highlighted fields. %{messages}"
       terms_not_accepted: Please accept Terms and Conditions
       required: Field cannot be blank
       invalid_number: "Please enter a valid phone number"

spec/system/consumer/split_checkout_spec.rb

@@ -294,6 +294,7 @@ describe "As a consumer, I want to checkout my order" do
           click_button "Next - Payment method"
 
           expect(page).to have_content "Saving failed, please update the highlighted fields."
+          expect(page).to have_content "Ship address address1 can't be blank"
           expect(page).to have_content "Shipping address same as billing address?"
           expect(page).to have_content "Save as default shipping address"
           expect(page).to have_checked_field "Shipping address same as billing address?"