Fix invite banner display for subgroups

Makes the "Invite your colleagues" banner display for a subgroup
with the same member count rules as a parent group.

Changelog: fixed

app/helpers/groups_helper.rb

@@ -230,7 +230,7 @@ module GroupsHelper
   end
 
   def multiple_members?(group)
-    group.member_count > 1
+    group.member_count > 1 || group.members_with_parents.count > 1
   end
 
   def get_group_sidebar_links

changelogs/unreleased/fix-invite-banner-for-subgroups.yml

+---
+title: 'Fix invite banner display member count for subgroups page'
+merge_request: 59948
+author:
+type: fixed

spec/helpers/groups_helper_spec.rb

@@ -420,13 +420,13 @@ RSpec.describe GroupsHelper do
   describe '#show_invite_banner?' do
     let_it_be(:current_user) { create(:user) }
     let_it_be_with_refind(:group) { create(:group) }
+    let_it_be(:subgroup) { create(:group, parent: group) }
     let_it_be(:users) { [current_user, create(:user)] }
 
-    subject { helper.show_invite_banner?(group) }
-
     before do
       allow(helper).to receive(:current_user) { current_user }
       allow(helper).to receive(:can?).with(current_user, :admin_group, group).and_return(can_admin_group)
+      allow(helper).to receive(:can?).with(current_user, :admin_group, subgroup).and_return(can_admin_group)
       users.take(group_members_count).each { |user| group.add_guest(user) }
     end
 
@@ -440,17 +440,39 @@ RSpec.describe GroupsHelper do
     end
 
     with_them do
-      context 'when the group was just created' do
-        before do
-          flash[:notice] = "Group #{group.name} was successfully created"
+      context 'for a parent group' do
+        subject { helper.show_invite_banner?(group) }
+
+        context 'when the group was just created' do
+          before do
+            flash[:notice] = "Group #{group.name} was successfully created"
+          end
+
+          it { is_expected.to be_falsey }
         end
 
-        it { is_expected.to be_falsey }
+        context 'when no flash message' do
+          it 'returns the expected result' do
+            expect(subject).to eq(expected_result)
+          end
+        end
       end
 
-      context 'when no flash message' do
-        it 'returns the expected result' do
-          expect(subject).to eq(expected_result)
+      context 'for a subgroup' do
+        subject { helper.show_invite_banner?(subgroup) }
+
+        context 'when the subgroup was just created' do
+          before do
+            flash[:notice] = "Group #{subgroup.name} was successfully created"
+          end
+
+          it { is_expected.to be_falsey }
+        end
+
+        context 'when no flash message' do
+          it 'returns the expected result' do
+            expect(subject).to eq(expected_result)
+          end
         end
       end
     end