keep quiz assignment group in sync when dragging on assignment index

test plan:
 - create two quizzes in separate assignment groups
 - on the assignments index page, drag a quiz into a different
   assignment group
 - go to the quiz page and ensure the assignment group shown
   is up to date

fixes CNVS-39620

Change-Id: I639aa19b37e08fc63b91fa295db4ff575c4e48f4

app/controllers/assignment_groups_controller.rb

@@ -166,6 +166,7 @@ class AssignmentGroupsController < ApplicationController
       return render_unauthorized_action unless can_reorder_assignments?(assignments, @group)
 
       assignments.update_all(assignment_group_id: @group.id)
+      @context.active_quizzes.where(assignment_id: order).update_all(assignment_group_id: @group.id)
       @group.assignments.first.update_order(order) unless @group.assignments.empty?
       groups = AssignmentGroup.where(id: group_ids)
       groups.touch_all

spec/controllers/assignment_groups_controller_spec.rb

@@ -352,6 +352,16 @@ describe AssignmentGroupsController do
       expect(@group1.assignments.count).to eq(3)
     end
 
+    it 'moves an associated Quiz to the correct assignment group along with the assignment' do
+      @quiz = @course.quizzes.create!(title: 'teh quiz', quiz_type: 'assignment', assignment_group_id: @group2)
+      user_session(@teacher)
+      post :reorder_assignments, params: {course_id: @course.id, assignment_group_id: @group1.id,
+                                          order: @order + ",#{@quiz.assignment.id}" }
+      @quiz.reload
+      expect(@quiz.assignment.assignment_group_id).to eq(@group1.id)
+      expect(@quiz.assignment_group_id).to eq(@group1.id)
+    end
+
     context 'with grading periods' do
       before :once do
         group = Factories::GradingPeriodGroupHelper.new.create_for_account(@course.root_account)