Add test case that assigning belongs_to on destroyed object raises frozen error

This is to ensure that the behavior has not changed before and after
#31575.

1 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/test/cases/associations/belongs_to_associations_test.rb b/activerecord/test/cases/associations/belongs_to_associations_test.rb
index 6b4f826766..a85b56ac4b 100644
--- a/activerecord/test/cases/associations/belongs_to_associations_test.rb
+++ b/activerecord/test/cases/associations/belongs_to_associations_test.rb
@@ -37,6 +37,13 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal companies(:first_firm).name, firm.name
   end
 
+  def test_assigning_belongs_to_on_destroyed_object
+    client = Client.create!(name: "Client")
+    client.destroy!
+    assert_raise(frozen_error_class) { client.firm = nil }
+    assert_raise(frozen_error_class) { client.firm = Firm.new(name: "Firm") }
+  end
+
   def test_missing_attribute_error_is_raised_when_no_foreign_key_attribute
     assert_raises(ActiveModel::MissingAttributeError) { Client.select(:id).first.firm }
   end