Add regression test for setting inverse instances on normal & polymorphic...

Add regression test for setting inverse instances on normal & polymorphic relationships when building objects on new records

activerecord/test/cases/associations/has_many_associations_test.rb

@@ -241,6 +241,13 @@ def test_create_from_association_with_nil_values_should_work
     assert_equal "defaulty", bulb.name
   end
 
+  def test_build_from_association_sets_inverse_instance
+    car = Car.new(name: "honda")
+
+    bulb = car.bulbs.build
+    assert_equal car, bulb.car
+  end
+
   def test_do_not_call_callbacks_for_delete_all
     car = Car.create(name: "honda")
     car.funky_bulbs.create!
@@ -2146,6 +2153,13 @@ def test_build_with_polymorphic_has_many_does_not_allow_to_override_type_and_id
     assert_equal "Post", tagging.taggable_type
   end
 
+  def test_build_from_polymorphic_association_sets_inverse_instance
+    post = Post.new
+    tagging = post.taggings.build
+
+    assert_equal post, tagging.taggable
+  end
+
   def test_dont_call_save_callbacks_twice_on_has_many
     firm = companies(:first_firm)
     contract = firm.contracts.create!