Add feature flag for alert deprecation [RUN ALL RSPEC] [RUN AS-IF-FOSS]

app/controllers/projects/alert_management_controller.rb

@@ -3,6 +3,10 @@
 class Projects::AlertManagementController < Projects::ApplicationController
   before_action :authorize_read_alert_management_alert!
 
+  before_action(only: [:index]) do
+    push_frontend_feature_flag(:managed_alerts_deprecation, @project)
+  end
+
   feature_category :incident_management
 
   def index

config/feature_flags/development/managed_alerts_deprecation.yml

+---
+name: managed_alerts_deprecation
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/62528
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/331863
+milestone: '14.0'
+type: development
+group: group::monitor
+default_enabled: false

spec/features/alert_management/alert_management_list_spec.rb

@@ -55,4 +55,28 @@ RSpec.describe 'Alert Management index', :js do
       it_behaves_like 'alert page with title, filtered search, and table'
     end
   end
+
+  describe 'managed_alerts_deprecation feature flag' do
+    subject { page }
+
+    before do
+      stub_feature_flags(managed_alerts_deprecation: feature_flag_value)
+      sign_in(developer)
+
+      visit project_alert_management_index_path(project)
+      wait_for_requests
+    end
+
+    context 'feature flag on' do
+      let(:feature_flag_value) { true }
+
+      it { is_expected.to have_pushed_frontend_feature_flags(managedAlertsDeprecation: true) }
+    end
+
+    context 'feature flag off' do
+      let(:feature_flag_value) { false }
+
+      it { is_expected.to have_pushed_frontend_feature_flags(managedAlertsDeprecation: false) }
+    end
+  end
 end