Fix `CollectionProxy#concat` to return self by alias it to `#<<`

Formerly it was returning arguments (`records` array).

2 files changed, 4 insertions, 2 deletions

diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 4c9e4d0ad2..5fdc5a92fc 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -996,9 +996,10 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
     assert_predicate companies(:first_firm).clients_of_firm, :loaded?
 
-    companies(:first_firm).clients_of_firm.concat([Client.new("name" => "Natural Company"), Client.new("name" => "Apple")])
+    result = companies(:first_firm).clients_of_firm.concat([Client.new("name" => "Natural Company"), Client.new("name" => "Apple")])
     assert_equal 4, companies(:first_firm).clients_of_firm.size
     assert_equal 4, companies(:first_firm).clients_of_firm.reload.size
+    assert_equal companies(:first_firm).clients_of_firm, result
   end
 
   def test_transactions_when_adding_to_persisted
diff --git a/activerecord/test/cases/associations/has_many_through_associations_test.rb b/activerecord/test/cases/associations/has_many_through_associations_test.rb
index 0133beccec..0ac56c6168 100644
--- a/activerecord/test/cases/associations/has_many_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -242,9 +242,10 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   def test_concat
     person = people(:david)
     post   = posts(:thinking)
-    post.people.concat [person]
+    result = post.people.concat [person]
     assert_equal 1, post.people.size
     assert_equal 1, post.people.reload.size
+    assert_equal post.people, result
   end
 
   def test_associate_existing_record_twice_should_add_to_target_twice