SignUpUser raises error if validation fails

These errors are rescued in the ApplicationController.

You may also want to extract the API-specific code in
ApplicationController (lines 4-8) into a separate ApiController that
your API controllers inherit from.  This is a good idea if you plan to
have a frontend Rails app, such as an admin portal.

app/controllers/application_controller.rb

@@ -2,4 +2,8 @@ class ApplicationController < ActionController::Base
   # Prevent CSRF attacks by raising an exception.
   # For APIs, you may want to use :null_session instead.
   protect_from_forgery with: :null_session
+
+  rescue_from ActiveRecord::RecordInvalid do |exception|
+    render json: { errors: exception.message }, status: :unprocessable_entity
+  end
 end

app/controllers/v1/users_controller.rb

@@ -1,13 +1,7 @@
 class V1::UsersController < V1::ApplicationController
   def create
     user = SignUpUser.perform(user_params)
-
-    if user.save
-      render json: user, serializer: AuthenticationSerializer, root: :user
-    else
-      render json: { errors: user.errors.full_messages },
-             status: :unprocessable_entity
-    end
+    render json: user, serializer: AuthenticationSerializer, root: :user
   end
 
   private

app/services/sign_up_user.rb

@@ -32,6 +32,7 @@ def password
   def sign_up_user
     user.tap do |user|
       user.reset_token!
+      user.save!
     end
   end
 

spec/requests/v1/users_requests_spec.rb

@@ -33,7 +33,7 @@
           post(users_url, user_attributes, accept_headers)
 
           expect(response).to have_http_status :unprocessable_entity
-          expect(json_value_at_path('errors/0')).to eq 'Email has already been taken'
+          expect(json_value_at_path('errors')).to eq 'Validation failed: Email has already been taken'
         end
       end
     end

spec/services/sign_up_user_spec.rb

@@ -18,13 +18,12 @@
 
     context 'with invalid parameters' do
       context 'such as a preexisting email' do
-        it 'does not persist the user' do
+        it 'raises an error' do
           create(:user, email: email_attributes[:email])
 
-          result = SignUpUser.perform(email_attributes)
-
-          expect(result).to be_a User
-          expect(result).not_to be_persisted
+          expect {
+            SignUpUser.perform(email_attributes)
+          }.to raise_error ActiveRecord::RecordInvalid
         end
       end
     end