Merge pull request #34203 from albertoalmagro/add-habtm-singular-ids-regression-test

Add regression test against has_and_belong_to_many memoized singular_ids

activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb

@@ -25,6 +25,8 @@
 require "models/member"
 require "models/membership"
 require "models/sponsor"
+require "models/lesson"
+require "models/student"
 require "models/country"
 require "models/treaty"
 require "models/vertex"
@@ -780,6 +782,16 @@ def test_assign_ids_ignoring_blanks
     assert_equal [projects(:active_record), projects(:action_controller)].map(&:id).sort, developer.project_ids.sort
   end
 
+  def test_singular_ids_are_reloaded_after_collection_concat
+    student = Student.create(name: "Alberto Almagro")
+    student.lesson_ids
+
+    lesson = Lesson.create(name: "DSI")
+    student.lessons << lesson
+
+    assert_includes student.lesson_ids, lesson.id
+  end
+
   def test_scoped_find_on_through_association_doesnt_return_read_only_records
     tag = Post.find(1).tags.find_by_name("General")