Add GraphQL mutation tests

ee/changelogs/unreleased/231332-epics-not-inheriting-dates.yml

+---
+title: Update epic inherited dates and create notes when reordering in epic tree
+merge_request: 39742
+author:
+type: fixed

ee/spec/requests/api/graphql/mutations/epic_tree/reorder_spec.rb

@@ -51,7 +51,7 @@ RSpec.describe 'Updating an epic tree' do
 
   context 'when epic feature is enabled' do
     before do
-      stub_licensed_features(epics: true)
+      stub_licensed_features(epics: true, subepics: true)
     end
 
     context 'when the user does not have permission' do
@@ -141,6 +141,24 @@ RSpec.describe 'Updating an epic tree' do
             expect(mutation_response['errors']).to eq(["The sibling object's parent must match the current parent epic."])
           end
         end
+
+        context 'when the new parent is another epic and subepics feature is disabled' do
+          let(:new_parent_id) { GitlabSchema.id_from_object(base_epic).to_s }
+
+          before do
+            stub_licensed_features(epics: true, subepics: false)
+            other_epic = create(:epic, group: group)
+            epic2.update(parent: other_epic)
+          end
+
+          it_behaves_like 'a mutation that does not update the tree'
+
+          it 'returns the error message' do
+            post_graphql_mutation(mutation, current_user: current_user)
+
+            expect(mutation_response['errors']).to eq(['You don\'t have permissions to move the objects.'])
+          end
+        end
       end
 
       context 'when moving an issue' do