Twilio delivery method allows Notifier to handle errors (#444)

* Twilio delivery method allows Notifier to handle errors

* Add an example how to handle Twilio error

Author: bibstha

docs/delivery_methods/twilio_messaging.md

@@ -38,6 +38,23 @@ deliver_by :twilio_messaging do |config|
 end
 ```
 
+## Error Handling
+
+```ruby
+deliver_by :twilio_messaging do |config|
+  config.error_handler = lambda do |twilio_error_response|
+    error_hash = JSON.parse(twilio_error_response.body)
+    case error_hash["code"]
+    when 21211
+      # The 'To' number is not a valid phone number.
+      # Write your error handling code
+    else
+      raise "Unhandled Twilio error: #{error_hash}"
+    end
+  end
+end
+```
+
 ## Options
 
 * `json` - *Optional*

lib/noticed/delivery_methods/twilio_messaging.rb

@@ -3,6 +3,12 @@ module DeliveryMethods
     class TwilioMessaging < DeliveryMethod
       def deliver
         post_request url, basic_auth: {user: account_sid, pass: auth_token}, form: json.stringify_keys
+      rescue Noticed::ResponseUnsuccessful => exception
+        if exception.response.code.start_with?("4") && config[:error_handler]
+          notification.instance_exec(exception.response, &config[:error_handler])
+        else
+          raise
+        end
       end
 
       def json

test/delivery_methods/twilio_messaging_test.rb

@@ -3,7 +3,7 @@
 class TwilioMessagingTest < ActiveSupport::TestCase
   setup do
     @delivery_method = Noticed::DeliveryMethods::TwilioMessaging.new
-    set_config(
+    @config = {
       account_sid: "acct_1234",
       auth_token: "token",
       json: -> {
@@ -13,7 +13,8 @@ class TwilioMessagingTest < ActiveSupport::TestCase
           Body: "Hello world"
         }
       }
-    )
+    }
+    set_config(@config)
   end
 
   test "sends sms" do
@@ -38,6 +39,26 @@ class TwilioMessagingTest < ActiveSupport::TestCase
     end
   end
 
+  test "passes error to notification instance if error_handler is configured" do
+    @delivery_method = Noticed::DeliveryMethods::TwilioMessaging.new(
+      "delivery_method_name",
+      noticed_notifications(:one)
+    )
+
+    error_handler_called = false
+    @config[:error_handler] = lambda do |twilio_error_message|
+      error_handler_called = true
+    end
+    set_config(@config)
+
+    stub_request(:post, "https://api.twilio.com/2010-04-01/Accounts/acct_1234/Messages.json").to_return(status: 422)
+    assert_nothing_raised do
+      @delivery_method.deliver
+    end
+
+    assert(error_handler_called, "Handler is called if status is 4xx")
+  end
+
   private
 
   def set_config(config)