master courses: don't delete non-empty assignment groups

test plan:
* have a blueprint course with an assignment group
 and an assignment
* sync to an associated course
* add an assignment to the group in the associated course
* delete the group in the blueprint course
* re-sync
* it should not delete the group in the associated course

closes #ADMIN-827

Change-Id: Ibeab4fe7209ca4d726476935776227457534dc2c
Reviewed-on: https://gerrit.instructure.com/142556
Tested-by: Jenkins
Reviewed-by: Mysti Sadler <[email protected]>
QA-Review: Deepeeca Soundarrajan <[email protected]>
Product-Review: James Williams  <[email protected]>

app/models/content_migration.rb

@@ -607,7 +607,12 @@ def process_master_deletions(deletions)
       end
       item_scope.each do |content|
         child_tag = master_course_subscription.content_tag_for(content)
-        if child_tag.downstream_changes.any? && !content.editing_restricted?(:any)
+        skip_item = child_tag.downstream_changes.any? && !content.editing_restricted?(:any)
+        if content.is_a?(AssignmentGroup) && !skip_item && content.assignments.active.exists?
+          skip_item = true # don't delete an assignment group if an assignment is left (either they added one or changed one so it was skipped)
+        end
+
+        if skip_item
           Rails.logger.debug("skipping deletion sync for #{content.asset_string} due to downstream changes #{child_tag.downstream_changes}")
           add_skipped_item(child_tag)
         else

spec/models/master_courses/master_migration_spec.rb

@@ -419,6 +419,43 @@ def run_master_migration(opts={})
       expect(quiz_to.reload.quiz_questions.where(:migration_id => mig_id(@new_qq)).first).to_not be_nil
     end
 
+    it "shouldn't delete an assignment group if it's not empty downstream" do
+      @copy_to = course_factory
+      sub = @template.add_child_course!(@copy_to)
+
+      ag1 = @copy_from.assignment_groups.create!(:name => "group1")
+      a1 = @copy_from.assignments.create!(:title => "assmt1", :assignment_group => ag1)
+      ag2 = @copy_from.assignment_groups.create!(:name => "group2")
+      a2 = @copy_from.assignments.create!(:title => "assmt2", :assignment_group => ag2)
+      ag3 = @copy_from.assignment_groups.create!(:name => "group3")
+      a3 = @copy_from.assignments.create!(:title => "assmt3", :assignment_group => ag3)
+
+      run_master_migration
+
+      ag1_to = @copy_to.assignment_groups.where(:migration_id => mig_id(ag1)).first
+      a1_to = ag1_to.assignments.first
+      ag2_to = @copy_to.assignment_groups.where(:migration_id => mig_id(ag2)).first
+      a2_to = ag2_to.assignments.first
+      ag3_to = @copy_to.assignment_groups.where(:migration_id => mig_id(ag3)).first
+      a3_to = ag3_to.assignments.first
+
+      Timecop.freeze(30.seconds.from_now) do
+        [ag1, ag2, ag3].each(&:destroy!)
+        a2_to.update_attribute(:name, "some other downstream name")
+        @new_assmt = @copy_to.assignments.create!(:title => "a new assignment created downstream", :assignment_group => ag3_to)
+      end
+
+      run_master_migration
+
+      expect(ag1_to.reload).to be_deleted # should still delete
+      expect(a1_to.reload).to be_deleted
+      expect(ag2_to.reload).to_not be_deleted # should skip deletion because a2's deletion was skipped
+      expect(a2_to.reload).to_not be_deleted
+      expect(ag3_to.reload).to_not be_deleted # should skip deletion because of @new_assmt
+      expect(a3_to.reload).to be_deleted # but should have still deleted the assigment
+      expect(@new_assmt.reload).to_not be_deleted
+    end
+
     it "should sync unpublished quiz points possible" do
       @copy_to = course_factory
       sub = @template.add_child_course!(@copy_to)