Add error handling around SNS API calls

app/controllers/barbeque/sns_subscriptions_controller.rb

@@ -18,11 +18,22 @@ def edit
 
   def create
     @sns_subscription = Barbeque::SNSSubscription.new(params.require(:sns_subscription).permit(:topic_arn, :job_queue_id, :job_definition_id))
-
-    if @sns_subscription.save
-      update_sqs_policy!
-      subscribe_topic!
-      redirect_to @sns_subscription, notice: 'SNS subscription was successfully created.'
+    if @sns_subscription.valid?
+      begin
+        subscribe_topic!
+      rescue Aws::SNS::Errors::AuthorizationError
+        @sns_subscription.errors[:topic_arn] << 'is not authorized'
+        @sns_topic_arns = fetch_sns_topic_arns
+        render :new
+      rescue Aws::SNS::Errors::NotFound
+        @sns_subscription.errors[:topic_arn] << 'is not found'
+        @sns_topic_arns = fetch_sns_topic_arns
+        render :new
+      else
+        @sns_subscription.save
+        update_sqs_policy!
+        redirect_to @sns_subscription, notice: 'SNS subscription was successfully created.'
+      end
     else
       render :new
     end
@@ -50,6 +61,8 @@ def destroy
 
   def fetch_sns_topic_arns
     sns_client.list_topics.topics.map(&:topic_arn)
+  rescue Aws::Errors::MissingCredentialsError, Aws::SNS::Errors::AuthorizationError
+    []
   end
 
   def update_sqs_policy!

spec/controllers/barbeque/sns_subscriptions_controller_spec.rb

@@ -57,6 +57,17 @@
       expect { post :create , params: { sns_subscription: attributes } }.
         to change { Barbeque::SNSSubscription.count }.by(1)
     end
+
+    context 'with NotFound error' do
+      it 'does not create a record and shows error message' do
+        expect(sqs_client).not_to receive(:get_queue_attributes)
+        expect(controller).to receive(:subscribe_topic!).and_raise(Aws::SNS::Errors::NotFound.new(self, 'not found'))
+        allow(controller).to receive(:fetch_sns_topic_arns).and_return([])
+        post :create , params: { sns_subscription: attributes }
+        expect(response).to render_template(:new)
+        expect(assigns(:sns_subscription).errors[:topic_arn]).to eq(['is not found'])
+      end
+    end
   end
 
   describe '#destroy' do