Fix RSpec/NoExpectationExample cop (#25103)

.rubocop_todo.yml

@@ -528,13 +528,6 @@ RSpec/MultipleMemoizedHelpers:
 RSpec/NestedGroups:
   Max: 6
 
-# Configuration parameters: AllowedPatterns.
-# AllowedPatterns: ^expect_, ^assert_
-RSpec/NoExpectationExample:
-  Exclude:
-    - 'spec/controllers/auth/registrations_controller_spec.rb'
-    - 'spec/services/precompute_feed_service_spec.rb'
-
 RSpec/PendingWithoutReason:
   Exclude:
     - 'spec/models/account_spec.rb'

spec/controllers/auth/registrations_controller_spec.rb

@@ -244,9 +244,26 @@ RSpec.describe Auth::RegistrationsController do
       end
     end
 
-    it 'does nothing if user already exists' do
+    context 'with an already taken username' do
+      subject do
+        Setting.registrations_mode = 'open'
+        post :create, params: { user: { account_attributes: { username: 'test' }, email: 'test@example.com', password: '12345678', password_confirmation: '12345678', agreement: 'true' } }
+      end
+
+      before do
         Fabricate(:account, username: 'test')
+      end
+
+      it 'responds with an error message about the username' do
         subject
+
+        expect(response).to have_http_status(:success)
+        expect(username_error_text).to eq(I18n.t('errors.messages.taken'))
+      end
+
+      def username_error_text
+        Nokogiri::Slop(response.body).css('.user_account_username .error').text
+      end
     end
 
     include_examples 'checks for enabled registrations', :create

spec/services/precompute_feed_service_spec.rb

@@ -19,7 +19,7 @@ RSpec.describe PrecomputeFeedService, type: :service do
 
     it 'does not raise an error even if it could not find any status' do
       account = Fabricate(:account)
-      subject.call(account)
+      expect { subject.call(account) }.to_not raise_error
     end
 
     it 'filters statuses' do