Added user_cap_reached? to Group

Added related rspecs.
Added new saas_user_cap Feature Flag.

Changelog: added
EE: true

app/models/group.rb

@@ -80,7 +80,7 @@ class Group < Namespace
   # debian_distributions and associated component_files must be destroyed by ruby code in order to properly remove carrierwave uploads
   has_many :debian_distributions, class_name: 'Packages::Debian::GroupDistribution', dependent: :destroy # rubocop:disable Cop/ActiveRecordDependent
 
-  delegate :prevent_sharing_groups_outside_hierarchy, to: :namespace_settings
+  delegate :prevent_sharing_groups_outside_hierarchy, :new_user_signups_cap, to: :namespace_settings
 
   accepts_nested_attributes_for :variables, allow_destroy: true
 

ee/app/models/ee/group.rb

@@ -474,6 +474,13 @@ module EE
       ::Feature.enabled?(:iteration_cadences, self, default_enabled: :yaml)
     end
 
+    def user_cap_reached?(requested_hosted_plan = nil)
+      return false unless ::Feature.enabled?(:saas_user_caps, self, default_enabled: :yaml)
+      return false unless new_user_signups_cap
+
+      new_user_signups_cap <= billable_members_count(requested_hosted_plan)
+    end
+
     private
 
     override :post_create_hook

ee/config/feature_flags/development/saas_user_caps.yml

+---
+name: saas_user_caps
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/66264
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/336251
+milestone: '14.1'
+type: development
+group: group::utilization
+default_enabled: false

ee/spec/models/ee/group_spec.rb

@@ -1491,6 +1491,56 @@ RSpec.describe Group do
     end
   end
 
+  describe '#user_cap_reached?' do
+    let(:new_user_signups_cap) { nil }
+
+    before do
+      allow(group.namespace_settings).to receive(:new_user_signups_cap).and_return(new_user_signups_cap)
+    end
+
+    subject(:user_cap_reached_for_group?) { group.user_cap_reached? }
+
+    context 'when the :saas_user_caps feature flag is not enabled' do
+      it { is_expected.to be_falsey }
+    end
+
+    context 'when the :saas_user_caps feature flag is enabled' do
+      before do
+        stub_feature_flags(saas_user_caps: true)
+      end
+
+      context 'when no user cap has been set' do
+        it { is_expected.to be_falsey }
+      end
+
+      context 'when a user cap has been set' do
+        let(:new_user_signups_cap) { 100 }
+
+        before do
+          allow(group).to receive(:billable_members_count).and_return(billable_members_count)
+        end
+
+        context 'when this cap is higher than the number of billable members' do
+          let(:billable_members_count) { new_user_signups_cap - 10 }
+
+          it { is_expected.to be_falsey }
+        end
+
+        context 'when this cap is the same as the number of billable members' do
+          let(:billable_members_count) { new_user_signups_cap }
+
+          it { is_expected.to be_truthy }
+        end
+
+        context 'when this cap is lower than the number of billable members' do
+          let(:billable_members_count) { new_user_signups_cap + 10 }
+
+          it { is_expected.to be_truthy }
+        end
+      end
+    end
+  end
+
   it_behaves_like 'can move repository storage' do
     let_it_be(:container) { create(:group, :wiki_repo) }