Implement and test private method all_timestamp_attributes_in_model

Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

activerecord/lib/active_record/timestamp.rb

@@ -74,6 +74,10 @@ def timestamp_attributes_for_update_in_model
       timestamp_attributes_for_update.select { |c| self.class.column_names.include?(c.to_s) }
     end
 
+    def all_timestamp_attributes_in_model
+      timestamp_attributes_for_create_in_model + timestamp_attributes_for_update_in_model
+    end
+
     def timestamp_attributes_for_update #:nodoc:
       [:updated_at, :updated_on]
     end

activerecord/test/cases/timestamp_test.rb

@@ -165,4 +165,9 @@ def test_timestamp_attributes_for_update_in_model
     toy = Toy.first
     assert_equal toy.send(:timestamp_attributes_for_update_in_model), [:updated_at]
   end
+
+  def test_all_timestamp_attributes_in_model
+    toy = Toy.first
+    assert_equal toy.send(:all_timestamp_attributes_in_model), [:created_at, :updated_at]
+  end
 end