Raise an error when the transaction is invalid

Instead of displaying the errors object's to_s, show the actual
validation errors.

app/controllers/solidus_paypal_braintree/transactions_controller.rb

@@ -1,4 +1,6 @@
 class SolidusPaypalBraintree::TransactionsController < Spree::StoreController
+  class InvalidTransactionError < StandardError; end
+
   PERMITTED_BRAINTREE_TRANSACTION_PARAMS = [
     :nonce,
     :payment_type,
@@ -23,7 +25,8 @@ def create
         return redirect_to spree.checkout_state_path(import.order.state)
       end
     else
-      render text: transaction.errors
+      raise InvalidTransactionError,
+        "Transaction invalid: #{transaction.errors.full_messages.join(', ')}"
     end
   end
 

spec/controllers/solidus_paypal_braintree/transactions_controller_spec.rb

@@ -78,9 +78,11 @@
     context "when the transaction is invalid" do
       before { params[:transaction].delete(:phone) }
 
-      it "displays the errors object" do
-        subject
-        expect(response.body).to match(/^#<ActiveModel::Errors:0x[\w]{14}>$/)
+      it "raises an error" do
+        expect { post_create }.to raise_error(
+          SolidusPaypalBraintree::TransactionsController::InvalidTransactionError,
+          "Transaction invalid: Phone can't be blank"
+        )
       end
     end
   end