Make sure we always return an array of hierarchies

Even when we pass an array of only a single object

app/serializers/group_child_serializer.rb

@@ -28,7 +28,9 @@ class GroupChildSerializer < BaseSerializer
       represent_hierarchy(children.hierarchy(hierarchy_root), opts).first
     else
       hierarchies = GroupDescendant.build_hierarchy(children, hierarchy_root)
-      represent_hierarchy(hierarchies, opts)
+      # When an array was passed, we always want to represent an array.
+      # Even if the hierarchy only contains one element
+      represent_hierarchy(Array.wrap(hierarchies), opts)
     end
   end
 

spec/controllers/groups/children_controller_spec.rb

@@ -141,6 +141,15 @@ describe Groups::ChildrenController do
           expect(response).to have_http_status(200)
         end
 
+        it 'returns an array with one element when only one result is matched' do
+          create(:project, :public, namespace: group, name: 'match')
+
+          get :index, group_id: group.to_param, filter: 'match', format: :json
+
+          expect(json_response).to be_kind_of(Array)
+          expect(json_response.size).to eq(1)
+        end
+
         it 'returns an empty array when there are no search results' do
           subgroup = create(:group, :public, parent: group)
           l2_subgroup = create(:group, :public, parent: subgroup)

spec/serializers/group_child_serializer_spec.rb

@@ -95,6 +95,15 @@ describe GroupChildSerializer do
           expect(project1_json[:id]).to eq(project1.id)
           expect(project2_json[:id]).to eq(project2.id)
         end
+
+        it 'returns an array when an array of a single instance was given' do
+          project = create(:project, namespace: parent)
+
+          json = serializer.represent([project])
+
+          expect(json).to be_kind_of(Array)
+          expect(json.size).to eq(1)
+        end
       end
     end
   end